关于直升机活塞式发动机的功率与效率（）.
A.旋翼消耗功率90%左右
B.效率在95%以上
C.尾桨在悬停时消耗功率最少
参考答案：A
His uncle ______ for more than 9 years.[ ]
A. has come here
B. has started to work
C. has lived there
D. has left the university
儿童理想的血铅水平为（）
A.1.2μmol／L
B.1.1μmol/L
C.0.6μmol／L
D.0.48μmol／L
E.0μmol／L
