题目内容：

they have been trying to find out how the fire began.句子成分怎么分...?how the fire began是find out的宾语,那从整个句子来看成分怎么分呢?谢谢.

优质解答

主 谓 宾 [ 宾语从句]
（they ）（have been trying） （to find out [how the fire began].）
to find out how the fire began 动词不定式在整个句子中作宾语