脑血管畸形突然倒地，昏迷，脉搏52次／分，双瞳孔不等大，左：右=4mm：2mm，右侧锥体束征阳性。诊断首先考虑（）。

A.小脑幕切迹疝

B.小脑扁桃体疝

C.视神经损伤

D.颅内低压

E.原发性脑干损伤

The teacher was angry about his being late for class, but he behaved ______ nothing had happened.

A．as

B．even if

C．as if

D．even though