Who could tell ___ his son’s circumstances really was. ?

The sentence "Who could tell ___ his son’s circumstances really was" requires a word that introduces a clause providing clarification or explanation about the son’s circumstances. Among the options providedA) which, B) that, C) why, and D) whatonly D) "what" effectively fits this context.

Using "what" here suggests that the speaker is inquiring into the nature or details of the son’s circumstances. The phrase implies that there is an unknown quality or state of affairs regarding the son that needs to be elucidated. For example, it indicates a desire to uncover the truth or reality behind the circumstances.

In contrast, option A) "which" implies a selection among defined choices, which doesn’t apply in this context. B) "that" could theoretically work, but it does not capture the nuance of discovering the essence of the circumstances, while C) "why" asks for a reason rather than a description. Thus, "what" is the most suitable option, as it opens the door to clarifying and understanding what the son's circumstances actually entail.