问题描述： He is doing his homework为什么该句中的doing用原形 1个回答 分类：英语 2014-12-10 问题解答： 我来补答 He is doing his homework.他正在做家庭作业.现在进行时态,be +动词现在分词.所以这要用do的－ing形式. 展开全文阅读
