—You missed the train?

—Yes.      I had gone by taxi.

A．If only

B．Only if

C．So long as

D．as long as

下列哪些是机械通气指征（）

A.重度脑水肿

B.呼吸困难伴发绀

C.呼吸不规则伴屏气

D.大量胸腔积液伴呼吸困难

E.血气分析示二氧化碳潴留