最难治的弱视是（）

A.斜视性弱视

B.屈光参差性弱视

C.形觉剥夺性弱视

D.屈光不正性弱视

E.成年后发现的弱视

I will never understand how it ______ that you failed in the examination for you are such a good student.

A．came about

B．brought in

C．stayed up

D．ended up