He ______________ to Beijing the day before yesterday. [ ]
A. go
B. went
C. going
D. goes
答案:B
下列物品中,通常情况下属于导体的是( )
A.绘画橡皮
B.食盐水
C.橡胶轮胎
D.塑料尺
体积为0.4m3,密度为2.5×103m3的石块,其重力是多大?画出重力的示意图,能否用最多承受5×105N的钢绳吊起?