请教这里为什么只能用Since,不能用When?

题目

请教这里为什么只能用Since,不能用When?
(Since) she was a child,she has lived in San Francisco.
1.请教这里为什么只能用Since,不能用When（当她是小孩子时,她住在旧金山）?原因是?
2.是不是有Since的句子,从句(she has lived in San Francisco)都要用现在完成时?

答案

如果用when,when she was a child,说的是过去时间,她小时候而这里用since she was a child,与后面用完成时态呼应,即：自从她小时候以来,就一直住在上海 例句：When she was child,she lived in Shanghai.她小时候住...