Although your son made some mistakes, he worked hard at his lessons. You shouldn’t be hard ______ him.

A．in

B．at

C．on

D．for

熄灭性ERG常见于哪些疾病，除了（）。

A.Leber先天性黑矇

B.视网膜发育不全

C.视网膜色素变性

D.全视网膜脱离

E.视网膜脉络膜炎