-When did the earthquake (地震) in Lushan happen?
-It happened __________ 8:02 __________ the morning of April 20, 2013.
A:on, in
B:at, in
C:at, on
D:on; on
刀、斧的风刃磨的很薄,是为了减小 ____ ,从而增大 ____ ;双脚站立的人,要使他对地面压强迅速增加一倍,只需 ____ .
如图为元素周期表第4周期的一部分.据此判断下列说法中错误的是( )