Only good swimmers can get to that place. There is water all ________ it.
A:for
B:around
C:at
D:from
—Which is more useful, reading or writing?
—I think _______ of them are useful.
2012年6月8日,科学家在某地观测一物体的日光成影状况,根据其影长的变化绘成示意图(下图)。据图判断,该地位于( )
如图,AB是⊙O的直径,C,D 是⊙O上的点,∠CDB=30°,过点C作⊙O的切线交AB的延长线于E,则sinE的值为( )