Clare finally decided to leave the company she__for since she graduated from university.A.would work B.has worked C.was working D.had worked工作不是在毕业之后蛮,可是后面毕业不是用了过去式,为什么工作要用过去完成时啊

Clare finally decided to leave the company she__for since she graduated from university.
A.would work B.has worked C.was working D.had worked
工作不是在毕业之后蛮,可是后面毕业不是用了过去式,为什么工作要用过去完成时啊