实数x，y满足·（ ）A. －2 B.4 C.4或－2 D. －4或2
小明和小雯一起打扫教室卫生，如图所示，他们提着一桶水沿水平方向匀速行走的过程中，以下说法错误的是（ ） A．水桶的重力没有做功 B．
--- You should have recited the text yesterday. --- _______. But I forgot all when asked to recite in front of many students. A. So I should B. So should I C.
已知函数f(x)= 则f［f()］的值是 （ ） A.9 B. C.－9
Business is improving but much more hard work and common sense will be _____ before any profits can be realized. A. put up with B. called for C. gone through
在下列几个实例中，机械能守恒的是（ ） A.在平衡力作用下运动的物体B.在粗糙水平面上下滑的物体，下滑过程中受到沿斜面向下的拉力，拉力大
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