我们看到太阳每天东升西落,主要是因为地球( )
A:自西向东自转
B:自西向东公转
C:自东向西自转
D:自东向西公转
—________ great fun we had at the party last night!
—Yes, it was so exciting that everyone was happy.
如图所示,墙上有两个钉子a和b,它们的连线与水平方向的夹角为37°,两者的高度差为L.一条不可伸长的轻质细绳一端固定于a点,另一端跨过光滑钉子b悬挂一质量为m1的重物.在绳ab段中点c有一固定细绳套.若细绳套上悬挂质量为m2的钩码,平衡后绳的ac段正好水平,则重物和钩码的质量比 m1m2 为( )
Because of the bad weather, the travelers had to stop, and decided to a tent for the night. ( )