小儿易发生肺部感染的最主要原因是()。
A.纤毛运动较差
B.支气管管腔狭小
C.呼吸中枢不健全
D.胸廓活动范围小,肺不能充分扩张
E.肺含血量多,含气量少
参考答案:E
Shortly after the accident two ____ policemen were sent to the spot to keep order.
A.score of
B.scores
C.score
D.scores of
沥青在使用前,置于熔解槽中,熔化温度一般150℃,其目的是什么?