C

本句是一个主从复合句，主句含有情态动词can，动作go还未发生，属于将来时；因此，when引导的时间状语从句要用现在时；当go动作发生时，finish动作已经完成了，故选 C。当然，空格出还可以用finish。如：

She will go to bed when she has done/ finishes her homework.

You can go to play football if you have finished your work.