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.—What has Tom been doing recently?
       —I don’t know.          care.
       A.nor I do              B.nor do I              C.neither am I         D.neither I am
22.How does it          that he is so badly-off when he earns quite a good salary?
       A.come out            B.come about          C.come up              D.come along