说明
appear, seem, etc. 之后的动词不定式的完成式
核心问题
... but this didn't appear to have caused the fire.
句中的 didn't appear to have caused 能否改为 didn't appear to cause?
词典解答
在 appear, seem 等动词后使用动词不定式的一般式和完成式,意义是不同的。这里需要牢牢记住:动词不定式的完成式所表达的动作是在谓语动词(appear, seem 等)之前发生的。请对比：