.My sister ________ (stay) in Beijing for three months last year.有一个“for”啊。还有、“因为是段时所以用完成时”是什么意思》?

问题描述:

.My sister ________ (stay) in Beijing for three months last year.
有一个“for”啊。
还有、“因为是段时所以用完成时”是什么意思》?