Which of the following is NOT the reason why the author says "being open is difficult"？A．B

Which of the following is NOT the reason why the author says "being open is difficult"？

A．Because it makes us feel easy to be attacked.

B．Because people don"t want others to know many details about themselves.

C．Because people are afraid of being against when they tell others their real opinions.

D．Because people cannot make sure whether others can be open to them in return.

请帮忙给出正确答案和分析，谢谢！