Which of the following italicized parts is NOT an object clause？A．I found it necessary tha

Which of the following italicized parts is NOT an object clause？

A．I found it necessary that we practise English every day.

B．She stood up and smiled as the headmaster came in.

C．Let"s see how we can raise our efficiency.

D．I"m not sure when she will leave for San Francisco.

请帮忙给出正确答案和分析，谢谢！