The correct answer is: B. “My son,” said Mr Robinson, “what do you want to be when you grow up?”
This is because the question is about what Mr Robinson’s son wants to be when he grows up, not about what he will be or what he did want to be. The use of the present tense “want” indicates that Mr Robinson is asking his son about his current desires, not about his past or future plans.
Option A is incorrect because it uses the future tense “will”. This indicates that Mr Robinson is asking his son about his future plans, not about his current desires.
Option C is incorrect because it uses the past tense “wanted”. This indicates that Mr Robinson is asking his son about his past desires, not about his current desires.
Option D is incorrect because it uses the modal verb “would”. This indicates that Mr Robinson is asking his son about his hypothetical desires, not about his actual desires.