Have you told him we have changed the plan?I have but I haven’t done it yet.A. mustB

问题补充：

--- Have you told him we have changed the plan?

I have, but I haven’t done it yet.

A. must

B. ought to

C. needn’t

D. can’t

答案：

A. must

(答案→)B. ought to

C. needn’t

D. can’t

解析：考察情态动词用法。A必须，一定；B应该；C不必；D不可能；ought to have done本应该做某事，实际上却做未。Must have done一定做了某事；needn’t have done本不需要做某事，实际上却做了。句意：—你告诉他我们改变计划了吗？—我本应该告诉他，但是我还没有告诉他呢。根据句意说明B正确。