第1个回答 2008-07-19
have been+动词ing...现在完成进行时------表示过去开始的事情延续到现在,并且还在继续进行中
Tom, you have been doing the task for a month, haven't you?
汤姆,这项工作你已做了一个月了,是吗?
was+现在分词 过去进行时--------当时正在做。。。表示过去某个时段正在进行的事
When he was doing underground work he was arrested because a renegade informed against him.他正在做地下工作时, 曾因叛徒告密而被捕。