You can't go out ( ) your homework is being done答案是until,bef

You can't go out ( ) your homework is being done.
我觉得答案应该是as.句意是：“你不能出去,【因为】你正在做作业”.
我觉得答案until不对,我们很容易跳进not...until这个陷阱,如果选until意思是：“你不能出去,直到你的作业【正在做】”,显然不通.
如果选before,句子应该是：You can't go out ( ) your homework has been done.