1.I have been in the middle school attached to Tongji University(下文简称MSTJ) for 3 years.
2.I came to MSTJ 3 years ago.
3.I have been a student of MSTJ for 3 years.
4.My elder brother has joined the army for 3 years.
5.My elder brother has been in the army for 3 years.
6.My elder brother has been a soldier for 3 years.
注：1.关于“附中”的说法,middle school attached to XX university比较麻烦但是标准
2.have been../done..后面加for some time表示保持一个状态有一段时间了；而一个动词的过去式应当加...ago/before这一类表示某个时间点之前.这种题目就是为了让你熟练掌握这种用法吧~