从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21．Today CCTV offers a _______of programmes to satisfy different needs and _______.
A．many; interests B．number; habits C．variety; tastes D．deal; likes
22．If we know more about _______causes the problem, we may take measures before it is _______late.
A．what; too B．which; very C．that; already D．that; so
