Which of the following pronouns is used as a formal subject？A．It was two o"clock in the mo

Which of the following pronouns is used as a formal subject？

A．It was two o"clock in the morning.

B．It was rebuilt on the site of the old building.

C．It was difficult to remember the name.

D．It was sunny and warm most of the time.

请帮忙给出正确答案和分析，谢谢！