Which of the following may be the most original reason for the problem of undergraduates m

Which of the following may be the most original reason for the problem of undergraduates mental-health？

A．Colleges are tough and many students couldn"t adjust themselves to it well.

B．Theye is the lack of enough counseling service to help troubled students out.

C．They think they"ll be labelled as the crazy kids because of their mental difficulty.

D．The overwhelming majority of troubled students are no threat to anyone but themselves.

请帮忙给出正确答案和分析，谢谢！