4 A: How many books ___________ (you/buy)? B: I only ___________ (buy) one.

Let's fill in the blanks with the correct form of the verbs in the past simple tense.

1. A: How many books did you buy?

   B: I only bought one.

Explanation:

• The question in the past simple requires the auxiliary verb 'did' and the base form of the verb 'buy'.
• The past simple form of 'buy' is 'bought'.