Tom sat down at his desk and began to do his homework.

Tom sat down at his desk and his homeork was begun to do .
如果不明白,请再问；如果对你有所帮助,
请点击本页面中的“选为满意回答”按钮,begun？？？对呀，begin　的过去分词是begun，被动语态的结构是be+动词的过去分词。