while being there he joined in voluntary labor on a project

问题描述:

while being there he joined in voluntary labor on a project
为什么 while 后面要用being there 而不是be there
如果这个句子不用省略的形式 改成完整形式 是不是这样?
while he was therehe joined in voluntary labor on a project?

此句中,while引导的动名词短语作主句he joined in voluntary labor on a project的时间状语,while引导的是短语,而不是句子.写成完整的形式while he was therehe joined in voluntary labor on a project 是这样没...