开放性喉外伤引发皮下气肿的常因为（）。
A.软骨骨折
B.咳嗽
C.喉阻塞
D.肺尖胸膜壁层撕裂
E.吞咽困难
参考答案：B
The children talked so loudly at dinner table that I had to struggle __________.
A．to be heard
B．to have heard
C．hearing
D．being heard
