只要是two weeks两个字分开写，后边就要用复数形式，意思是说两周。比如 1)I have been here for two weeks.我已经到这里两周了。

2)He left here two weeks ago.他两周前离开了这里。但是，如果two-week写在一起，中间加连字符-，这时它就成了合成形容词，此时用单数。比如a two-week holiday(一个两周的假期)