21£®When we saw from the plane£¬______ new- ­looking earth appeared before us£¬______ earth that we had never seen before.
A£®the£»the           B£®a£»an      C£®an£»the             D£®the£»an¡¡  

22. There are some _____when you have to change your mind just before doing it.

A£®situations    B£®occasions   C£®circumstances  D£®conditions