汽轮机升速中振动大的主要原因有（）。
A.暖机不充分
B.机内零部件松动
C.膨胀不匀
D.接近临界转速
参考答案：A, B, C, D
________ some people regard as a drawback is seen as a plus by many others．[ ]
A．Whether
B．What
C．That
D．How
正方形的边长扩大到它的3倍，它的面积就扩大到原面积的[ ]
A.3倍
B.6倍
C.9倍
D.12倍
