吗啡对中枢神经系统作用中，"中毒时瞳孔针尖样大小，与中脑盖前核有关"的作用为（）。

A.镇痛

B.镇咳

C.缩瞳

D.抑制呼吸

E.镇静和欣快感

If you have some difficulties ____ your grammar, you had better ask your teacher ____.

A．in; on some advice

B．for; for some advices

C．on; some advice

D．with; for some advice