Complete the sentence fragment: 'Why don't ()?'

• A. You should see a doctor
• B. You see a doctor
• C. You could see a doctor
• D. You will see a doctor

Answer: (B)

Forming a why-question in the present simple uses do-support. When you ask “Why don’t …?” the verb after the subject must be in its base form. Here, after don’t you need the base form of the verb, which is see. So the natural completion is “you see a doctor,” making the full question: “Why don’t you see a doctor?” This asks for the reason for not taking the action.

The other options wouldn’t fit because they introduce a different structure after don’t (should, could, or will) which isn’t allowed with do-support in this pattern, or they would create an ungrammatical construction.