Answer:
a. A questionnaire was distributed to the participants.
Step-by-step explanation:
The correct sentence in the set is "A questionnaire was distributed to the participants." Options B and C are both incorrect because of grammatical errors in the sentences.
In a sentence, 'a' is used to address a singular noun. Whenever there is a plural word, using the word 'a' to address the plural noun is incorrect. For instance, 'a questionnaire' is correct while 'a questionnaires' is incorrect.
Option C is also incorrect because after the word 'was', the word 'distributed' should have been used and not 'distribute' because the sentence is in simple past tense.