4. ______ your parents at the supermarket yesterday? – Yes, they ______.

Explanation:

This task involves forming a question and an answer in the past tense using the verb 'to be'. Since 'your parents' is a plural subject, we use 'were' for the question and 'were' for the affirmative answer.

Answers:

1. Were your parents at the supermarket yesterday? – Yes, they were.