从每题所给的A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21．Besides the others, there was still third one who said he was second to reach the end.
A．a; a B．a; the C．the; the D．the; a
22．The purpose of their explorations is as important to them as to us.
A．they are B．they have C．it is D．it has
23．Mike is handsome, kind and full of energy , I can’t speak too highly of him.
A．As a result B．By the way C．In a word D．On the contrary
