为了使用户能直观地读取数值，交流电能表加入了（）。
A．转速测量机构
B．积算机构
C．驱动机构
D．制动机构
参考答案：B
Which of the following statements about a callable bond is TRUE（）
A. The call option on a bond trades separately from the bond itself.
B. A bondholder usually loses if a bond is called by being forced to reinvest the proceeds at a lower interest rate.
C. Callable bonds follow the standard inverse relationship between interest rates and price.
试述压缩（4L-20/5）有闷声（如冲击的回声）的原因？
