Topic: Sentence (বাক্য),

Best Answer Explained in Below-:

In the context of the statement "I went to the library to take some books for my brother," the most relevant question to ask is "D) Why did you go to the library?" This question seeks to uncover the purpose behind the action of going to the library. The speaker already provides the reason in their statement: they went to the library specifically to take books for their brother.

In contrast, the other options serve different functions. Option A, "When did you go to the library?" would inquire about the time of the visit, which is not addressed in the original statement. Option B, "Who went to the library?" focuses on the subject of the action but is already known from the speaker's account. Finally, Option C, "Did you go to the library?" is a confirmation question that doesn't explore the intent or motivation behind the action.

Thus, asking "Why did you go to the library?" directly invites the speaker to elaborate on their reason for visiting, aligning perfectly with the information they provided about their purpose: to help their brother by obtaining books. This illustrates the essential connection between the question and the details in the statement, making option D the most appropriate choice.