12.In the diurnal type of tidal oscillation, the alternate rise and fall of sea level, a single high water and a single low water occur __ tidal day.
(A)each
(B)each of
(C)each of the
(D)of each
each应该怎么用呢?C为什么不对呢?谢谢!
37.Under (the certain) conditions, a rainbow appears at the end (of) a (rain shower) (in the quarter) of the sky opposite the Sun.
这题为什么选A呢?难道加定冠词不对吗?谢谢!