旋风分离器主要由三部分组成：内筒、（）。
A.外筒
B.倒锥体
C.入口
D.集尘器
参考答案：A, B
Many businesses must have been badly influenced during that financial crisis, ________?
A．haven’t they
B．didn’t they
C．must’t they
D．weren’t they
铁路信号装置一般分为哪几类？
