Not once has she given in to any difficulty in her life and that's _____ she is a strong­willed woman.

A．why

B．when

C．because

D．where

下列哪些是全身麻醉中发生上呼吸道梗阻的常见原因()

A．舌后坠

B．咽部分泌物堵塞

C．支气管痉挛

D．喉痉挛

E．中枢性呼吸抑制