how long has she been helping her husband?___she was a young woman.1 from then 2 since 3 for 4 by then 请问选择哪一个,及分别说出每个为什么对与错
问题描述：
how long has she been helping her husband?___she was a young woman.
1 from then 2 since 3 for 4 by then
请问选择哪一个,及分别说出每个为什么对与错
答
2 since
答
选2 since 自从她还是个年轻女子开始.用于现在完成进行时
1.From then 本身就是现在完成时或现在完成进行时的时间状语,then 与she was a young woman重复
3.for要加时间段,而she was a young woman 是时间点
4.by then 用于过去完成时