It looked as if he were ill for a long time.

It looked as if he were ill for a long time.
【正确答案】：were改为had been。
【题目解析】：

根据后面的时间状语"for a long time"可知表语从句"as if he were ill for a long time"中应该使用完成时态；再根据谓语动词looked可知：表语从句中应该使用过去完成时，故应改为had been。