Which of the following italicized parts is used as an object？A．He wants to tell us when he

Which of the following italicized parts is used as an object？

A．He wants to tell us when he will leave.

B．It has been decided when the meeting will be held.

C．What I want to know is when you can finish the experiment.

D．I have no idea when she will be back.

请帮忙给出正确答案和分析，谢谢！