为防止起重机倾覆而设置的（）
A、变幅限位器
B、力矩限制器
C、行走限位器
参考答案：B
—Bob, it's getting cold outside. _______ take a jacket with you?
—All right, Mum. [ ]
A. Why do you
B. Why not
C. Why did you
D. Why don't
如果r和t都大于0，现值利率因子PVIF(r，t)永远都大于0。( )
