1a.Did you know a famous animal-rights activist has criticized horseracing because of the dangers involved?

1b. Did you know a famous animal-rights activist have criticized horseracing because of the dangers involved?
Subject-verb agreemnet? I choose b.

2a. Peer editing academic papers require critical-thinking skills and diplomacy.
2b. Peer editing academic papers requires critical-thinking skills and diplomacy.
Subject-verb agreement? I choose a
3a. Vitamins that are sold in a health-food store are not regulated by the food and drug administration.
3b. Vitamins that are sold in a health-food store is not regulated by the foood and drug administration.
subject-verb agreement? I choose b
can someone see if I have this right.

1. b. is correct.

2. a. is incorrect. Subject is "editing" - a gerund, which is considered singular.

3. b. is incorrect. Subject is "Vitamins" - a plural noun, and it needs a plural verb. The clause "that are sold in a health-food store" is getting in your way and confusing you.

http://grammar.ccc.commnet.edu/grammar/sv_agr.htm

from http://grammar.ccc.commnet.edu/grammar/index2.htm

how come 1 can't be a

1a.Did you know a famous animal-rights activist has criticized horseracing because of the dangers involved?

1b. Did you know a famous animal-rights activist have criticized horseracing because of the dangers involved?
Subject-verb agreemnet? I choose b.

In this sentence, the main subject is "you," but the subject you're being asked about is in a subordinate clause. That subject is "activist" -- singular or plural??

so you use have when it is singular right that's why I choose b.

The form "have" is not to be used with 3rd person singular subjects; the form "has" needs to be used in that case.

You can say these:
I have
you have
we have
they have

But you must use "has" with all 3rd person singular subjects, such as he, she, it, "activist," or any other SINGULAR noun or pronoun.

http://www.whitesmoke.com/english-verbs-basic-terms.html
Scroll down to section 4 which identifies person (1st, 2nd, and 3rd) and number (singular and plural).

Sorry, I see the confusion now. My error in my first response for you.

1.a. is correct.

some athletes have taken drug tests to prove they are not on steroids.

vitamins that are sold in a heath-food store are not regulated by the Food and Drug Administration

vitamins that are sold in a health-food store are not regulated bye th food and drug Administration

which one of these sentences are a subject verb agreement

1a. Did you know a famous animal-rights activist has criticized horseracing because of the dangers involved?

Subject-verb agreement? Yes, you are correct. In this sentence, the subject "a famous animal-rights activist" is singular and agrees with the verb "has criticized."

2a. Peer editing academic papers require critical-thinking skills and diplomacy.

Subject-verb agreement? No, you might have made a mistake here. The correct sentence would be 2b. "Peer editing academic papers requires critical-thinking skills and diplomacy." The subject "peer editing" is singular, so it requires the verb "requires."

3a. Vitamins that are sold in a health-food store are not regulated by the food and drug administration.

Subject-verb agreement? Yes, you are correct. In this sentence, the subject "vitamins that are sold in a health-food store" is plural and agrees with the verb "are not regulated."

Well done on 1a and 3a! However, 2b is the correct answer for the subject-verb agreement in sentence 2. Keep up the good work!