My uncle . . . . . . . . go for a walk every morning. A. must B. should C. would D. used to

The correct answer is: used to.

The verb “used to” is used to talk about past habits or repeated actions that are no longer true. In this case, the speaker is saying that their uncle used to go for a walk every morning, but he no longer does.

The other options are not correct because they do not express the idea of a past habit or repeated action.

• The verb “must” is used to talk about obligations or requirements. In this case, the speaker is not saying that their uncle is obligated to go for a walk every morning.
• The verb “should” is used to talk about recommendations or suggestions. In this case, the speaker is not suggesting that their uncle should go for a walk every morning.
• The verb “would” is used to talk about possibilities or hypothetical situations. In this case, the speaker is not talking about a possibility or hypothetical situation.

I hope this helps!