一刚体受不平行的三个力作用而平衡时，这三个力的作用线必在同一平面上。
参考答案：错
Look! If we had begun to do the work yesterday morning, we _______ ourselves just like them．
A．would have enjoyed
B．were to enjoy
C．should enjoy
D．would be enjoying
各类实验动物应（），以防交叉感染。
A.分室饲养
B.分笼饲养
C.分盒饲养
D.分楼饲养
