欲使物料不沿斜面下滑，物料的下滑分力不得（）物料与带面间的摩擦力。
A.大于
B.小于
C.等于
D.无法确定
参考答案：A
—You may find the key to the math problem on page 107．
—Ah, it's so simple． I wonder why I _ of that．
A．hadn't thought
B．haven't thought
C．didn't think
D．wasn't thinking
电动机的主要保护装置有哪些？
