鼓风机电机部分振动、振幅范围≤（）mm。
A.0.09
B.0.04
C.0.075
D.0.08
参考答案：B
They _____ in a factory now, but they _____ there a year ago.[ ]
A. works; not worked
B. work; didn't work
C. works; isn't working
D. is working; works
求方程y"+y=4sinx的通解．
