SS7E机车一系弹簧装置是由（）和并联垂向油压减振器组成。
参考答案：螺旋圆弹簧加橡胶垫
— I've had a stomachache for two weeks.
— You ____ to the doctor when it started. [ ]
A. must go
B. should go
C. ought to have gone
D. might have gone
投资者可以通过买卖不同的股票来回避证券的非系统性风险。( )
