Option D: was/wanted is correct.
Explanation: The subject (his father) is singular, hence was will be used; and the sentence is describing an event in the past, hence wanted
Option A: was/wants is incorrect: The subject (his father) was a doctor in the past, and wants is in the present tense
Option B is incorrect: The subject, his father is in singular, so were (a plural) can't be used.
Option C is incorrect: will be and would want can be used for future tenses (to indicate an action happening in the future). Hence, logically and grammatically incorrect