不定式作目的状语：I stayed at home to have a good rest. 我在家里想好好休息一下。不定式作结果状语：I'm too tired to play football today. 我太疲劳今天不能踢球了。不定式作原因状语：She felt bad to think of the problem. 想到那个问题就让她不舒服。