鼠笼式电动机的启动方法有（）。
A.间接启动
B.直接启动
C.增压启动
D.降压启动
E.变压启动
参考答案：B, D
In the last few years, they ______ three major concerts. [ ]
A. have had
B. had had
C. had
在存货决策中，（）可以不考虑。
A.订货成本
B.固定订货成本
C.变动订货成本
D.变动储存成本
