I can’t imagine _______. ?

The sentence "I can’t imagine _______" is a statement that requires a completion that logically fits in the context of someone expressing disbelief or inability to conceive of a particular idea or scenario.

Let's analyze the options provided:

A) "why did he recommend him" implies a question regarding the reason behind a recommendation. It does not fit with the structure of "I can’t imagine," which needs something that connects directly to an action or subject rather than a query about reasons.

B) "who recommended him for training" offers a noun clause that acts as the object of the verb "imagine." It expresses curiosity about the identity of the recommender, which aligns with the speaker's difficulty in picturing that situation.

C) "when will he recommend me" poses a temporal question and does not grammatically fit into the idea of something one cannot imagine, as it implies a future event rather than a subject or concept.

D) "how will he recommend him" also denotes a future action that the speaker cannot envision, rather than an identity or fact.

In summary, option B is the correct choice because it directly conveys an uncertainty about not knowing who made a recommendation, fitting seamlessly into the context of the sentence and providing a clear subject for the imagination to grapple with.