until 引导时间状语从句，大体规则是“主将从线”即主句使用与将来相关时态，从句使用与现在相关时态。I won't go until he comes back.主句一般将来时从句一般现在时。The discussion won't end until a plan has come up.主句一般将来时从句现在完成时。
didn't/return
didn't/returned
