题目

Why he did not arrive on time was that he        and it was too late to catch the early bus. A．was oversleeping B．has oversleptC．overslept    D．had overslept   答案：D如图所示，A、B、C、三个物体叠放在水平桌面上，在 A的上面再加一个竖直向下的作用力，则C物体受到的力共有：                          A．2个   B．3个  C．4个   D．5个