25.______ for a long time,but he tried to catch up with his classmates at last.
A.Having been ill B.Being ill
C.He was ill D.Though ill
解析：本题容易出错的原因就是考生常误认为考查分词短语作状语。其实认真研读句子可以发现but所起的作用，but连接并列句，因此答案应该选C。不妨再考虑一下，去掉but后情况又如何呢？
答案：C
24.I seldom watch TV in the evening ______ I have nothing to do.
A.except B.except for
C.except when D.except that
解析：A、B两个选项后面都接名词或名词短语。根据句子中in the evening可以判断except后应该跟表示时间的从句。