Which of the following sentences includes a subject clause？A．A prosperity that had never b

Which of the following sentences includes a subject clause？

A．A prosperity that had never been seen before appears in the country.

B．He must answer the question whether he agrees to it or not.

C．He told me that he had told Mary about the meeting already

D．It is suggested that the work should be done with great care.

请帮忙给出正确答案和分析，谢谢！