You can often get old Cambridge FCE, CAE (now called C1 Advanced), C2 Proficiency, (previously known as Cambridge English Proficiency) and IELTS Practice Test Books (you need the version with answers) from libraries, bookshops, your relatives, colleagues or friends or on Amazon. (Don't get Cambridge IELTS Academic 11 or General 11, Cambridge CAE 5 or Cambridge FCE 5 or 6 as I have those). Then do all the Reading sections, giving yourself the same number of minutes to do each one as there are questions. Plus anything else you can find by doing a search on Google for:

'free B2 and C1 texts for multiple choice reading comprehension'

or something similar.

I found this site: https://www.usingenglish.com/comprehension/advanced.html

and chose this text (se limk) but there are 7 texts in all:

https://www.usingenglish.com/comprehension/23.html

also

https://www.test-guide.com/free-toefl-practice-tests.html check all the links

https://www.test-guide.com/courses/gre/lessons/gre-practice-exam-1/quizzes/gre-verbal-reasoning-practice-test-1

B2 level, some general exercises just to get started:

https://www.examenglish.com/FCE/fce_reading.html and then the links

https://www.examenglish.com/FCE/fce_reading_and_use_of_english_test2.htm

https://www.examenglish.com/FCE/fce_reading3.htm

https://www.examenglish.com/FCE/fce_reading_part1_test2.htm

https://www.examenglish.com/FCE/fce_reading_part3_test2.htm

now here are some short texts:

https://www.esl-lounge.com/student/first-certificate-reading-multiple-choice.php

And here are some longer ones, but don't give yourself too much time when you do these reading comprehension texts. For example, as we said, when there are 6 questions, you have 6 minutes. If there are 4 questions, this means 4 minutes. Do each reading comprehension, first without a dictionary. Then check the words you don't know and see if you want to change your answers. Then check the answers.

https://www.flo-joe.co.uk/fce/students/tests/FCE-Part-5-Multiple-Choice-Practice-Test.htm

https://www.flo-joe.co.uk/fce/students/tests/1part3.htm

https://www.flo-joe.co.uk/fce/students/tests/2part2.htm

https://www.flo-joe.co.uk/fce/students/tests/2part3.htm

https://www.flo-joe.co.uk/fce/students/tests/3part2.htm

https://www.flo-joe.co.uk/fce/students/tests/part2.htm

https://www.flo-joe.co.uk/fce/students/tests/part4.htm

https://www.learninginstitute.ch/pdfs/fce-reading-uebungen-tests-98.pdf

more difficult, C1

https://www.esl-lounge.com/student/toefl-reading.php

https://www.ets.org/toefl/ibt/prepare/practice_sets/reading/

http://www.examenglish.com/IELTS/IELTS_academic_reading1.htm

and then all the other texts on the right of the page, Academic Reading 2-9

http://www.examenglish.com/CAE/cae_reading1.htm

and then the other texts on the right of the page

http://www.examenglish.com/BEC/BEC_Higher_reading_part1.htm

and then the other one on the right (BEC Higher)

http://www.examenglish.com/PTE/pte_general_level4_reading1.htm

and then the other ones on the right, B2 and C2

https://www.examenglish.com/TOEFL/TOEFL_reading3.htm

not texts 1 and 2 please, but the other ones on the right, 4-8

http://www.examenglish.com/cpe/cpe_reading_part1.htm

and then the other ones on the right, 2-4

http://www.lofoya.com/Verbal-Test-Questions-and-Answers/Reading-Comprehension/l3p1

and then pages 2-12, text and questions

http://www.esl-lounge.com/student/proficiency/cpe-074-last-photo-reading-multiple-choice.php

http://www.ecenglish.com/learnenglish/lessons/ielts-practice-global-temperatures

http://www.myenglishpages.com/site_php_files/reading-public-debt.php

and the other sections under 'related materials'

http://www.esl-lounge.com/student/reading/4r3-mother-fined.php

https://www.esl-lounge.com/student/reading/4r1-air-base.php

https://www.esl-lounge.com/student/reading/4r5-siberian-winter.php

https://www.esl-lounge.com/student/reading/4r6-snake-bites-boy.php

https://www.esl-lounge.com/student/reading/4r65-advanced-reading-new-website.php

and all the texts here

https://www.esl-lounge.com/toefl-reading.php

https://www.esl-lounge.com/ielts-academic-reading.php

https://www.esl-lounge.com/proficiency-reading-multiple-choice.php

and all the texts at

https://www.esl-lounge.com/student/ielts-academic-reading.php

e.g.

https://www.esl-lounge.com/student/ielts/ielts001-academic-reading-1.php

and

https://www.esl-lounge.com/student/ielts/ielts008-academic-reading-8.php

https://www.myenglishpages.com/site_php_files/reading_obesity.php

http://www.english-online.org.uk/toeflfolder/toeflread1.php?name=TOEFL%20Reading%20test%201

http://www.tolearnenglish.com/free/full/reality/comprehension.php

http://www.ecenglish.com/learnenglish/lessons/reading-do-children-see-enough-culture

http://www.grammarbank.com/reading-comprehension-activity-5.html

https://www.usingenglish.com/comprehension/32.html

http://www.infosquares.com/readingcomprehension/

and then choose a text

https://www.usingenglish.com/comprehension/

https://www.usingenglish.com/comprehension/advanced.html

and choose a text like this:

https://www.usingenglish.com/comprehension/24.html

The sample text below on pages 9 and 10 may also be useful but not the tips

http://www.upscmantra.com/userfiles/documents/CSAT/Comprehension/CSAT%20-%20Reading%20Comprehension.pdf

https://learnenglishteens.britishcouncil.org/skills/reading/advanced-c1-reading

http://www.esl-lounge.com/student/reading-advanced.php

https://www.testprepreview.com/modules/readingtest2.htm

http://www.infosquares.com/readingcomprehension/esl-reading-comprehension1.html

https://www.ereadingworksheets.com/free-reading-worksheets/reading-comprehension-worksheets/

https://en.islcollective.com/resources/printables/worksheets_doc_docx/reading_with_10_multiple_choice_questions/intermediate-b1-reading/5615

https://www.usingenglish.com/comprehension/advanced.html

https://www.flo-joe.co.uk/cae/students/tests/1part3.htm

https://www.graduateshotline.com/toefl/reading-comprehension-test-1.html

https://www.examenglish.com/cpe/cpe_reading_part2.htm

https://www.flo-joe.co.uk/cpe/students/tests/read1p4.htm

https://www.usingenglish.com/comprehension/32.html

https://www.usingenglish.com/comprehension/29.html

Lots of texts and 3 levels, Easy, Moderate and Difficult

http://www.lofoya.com/Verbal-Test-Questions-and-Answers/Reading-Comprehension/l1p1

http://www.lofoya.com/Verbal-Test-Questions-and-Answers/Reading-Comprehension/l2p1

http://www.lofoya.com/Verbal-Test-Questions-and-Answers/Reading-Comprehension/l3p1

then click on pages, 2,3,4 etc for more questions and next text

https://www.etsglobal.org/Tests-Preparation/The-TOEFL-Family-of-Assessments/TOEFL-Sample-Tests/TOEFL-ITP-Sample-Test-Questions/Section-3-Reading-Comprehension

Here there are 24 questions. Choose an answer to number 1, check it with View the Correct Answer and go to Next at the top for the next question.

https://collegereadiness.collegeboard.org/sample-questions/reading/1

Useful tips

https://classroom.synonym.com/tricks-taking-multiplechoice-exam-8737068.html

Go to this page and click on one of the tests (e.g. Test 1). When you finish all the questions, click on Validate for score. Then go back to the first page and choose another Test.

http://www.greguide.com/gre-sample-tests.html

https://agendaweb.org/reading/reading-pdf-6

https://www.ngllife.com/upper-intadvanced

http://www.euroexam.com/sites/network/files/private/practice-tests/euro_c1/31_WEB_C1_QUP_Reading.pdf

http://www.euroexam.com/sites/network/files/private/practice-tests/euro_c1/33_web_c1_key_reading.pdf

https://www.graduateshotline.com/toefl/reading-comprehension-test-1.html

https://www.graduateshotline.com/toefl/reading-comprehension-test-2.html

https://www.graduateshotline.com/toefl/reading-comprehension-test-3.html

https://www.graduateshotline.com/sampletoefl3.html

https://www.graduateshotline.com/toefl_practice_test4.html

https://www.graduateshotline.com/toefl-practice-test-5.html

https://gre.graduateshotline.com/reading_comprehension_practice.html