21. His father is used to sleeping with the windows _______ and the lights _______ .
A. opening; on B. opened; off C. open; on D. opening; off
选C。考查with复合结构。句意为：他父亲习惯开着窗亮着灯睡觉。open为形容词，表示窗子开着的状态；on为副词，意为“亮着”。
22. _______ he is very young, _______ he knows a lot.
A. Although; yet B. Although; but
C. Although; or D. Although; but
选A。考查although的用法。although为连词，故不能与连词but、or连用，故排除B、C、D三项。yet为副词，可与although共同出现在一个句子中。句意为：虽然他很年轻，但他知道很多。
