为什么用since?my bother studied at the high school since he joined the army

为什么用since?my bother studied at the high school since he joined the army
为什么用since?
my bother studied at the high school since he joined the army

为什么用since?my bother studied at the high school since he joined the army
我的哥哥高中毕业后就去参军了

自从，自什么之后