They were walking along the shore _______ a huge wave appeared out of nowhere, sweeping them out to sea.

A．as

B．while

C．when

D．though

［此病例属于 104－105题］　　患者张某，60岁，既往有肺心病史10年，昨日突然出现极度呼吸困难，口唇发紫，烦躁不安，今晨又出现昏迷、血压下降，心律失常。

对张某保持气道通畅最好的方法是

A．协助拍背

B．雾化吸入

C．建立人工气道

D．控制感染

E．导管吸痰