资格股股东退股时,其相关资料由会计部门定期装订入档保管,保管期限为()。
A、三年
B、五年
C、十五年
D、永久保管
参考答案:D
_____ his homework in time, he had to stay up late into the night.
A.Finishing
B.Having finished
C.To finish
D.To have finished
按条件f对关系R进行选择,其关系代数表达式为( )。