Which of the following contains an adverbial clause of cause？（2012)A．I got a job as soon a

Which of the following contains an adverbial clause of cause？(2012)

A．I got a job as soon as I left university.

B．As there was no answer, I wrote again.

C．You must do the exercises as I show you.

D．Wealthy as he is, Mark is not a happy man.

请帮忙给出正确答案和分析，谢谢！