Do it? ?

The question "Do it?" implies a desire to initiate an action, and the response options provided give various interpretations of how to proceed with that action. Among these, option B, "Let it be done," stands out as the most appropriate.

This phrase serves as an imperative that suggests allowing or permitting something to happen, which aligns well with the question's context. It implies a passive acceptance of the action being carried out, suggesting not just permission but an acknowledgment that completion of the action is desirable or necessary.

In contrast, option A, "It is done by you," shifts the focus onto the individual responsible for the action, which is not quite suitable as a response to the prompt. Option C, "Let done it by me," contains grammatical errors and lacks clarity, detracting from its effectiveness. Finally, option D, "Let it by done (by you)," is also grammatically incorrect and does not convey a clear message.

Thus, option B is the best choice because it correctly captures a sense of permission and encourages the action to take place, clearly and effectively addressing the original inquiry.