手术后鼓励病人深呼吸，咳嗽的主要目的是
A．减轻伤口疼痛B．预防肺不张和肺部感染C．促进伤口愈合D．减少出血E．预防肺栓塞
参考答案：B
She is very happy ______ she has got many good friends.
A．or
B．because
C．unless
D．so
fermentation
