I can let you go, as long as you can finish this task by the deadline.
我可让你走,只要你在最后的限期前完成任务。
You had better wash those dirty clothes.
你该去把那些脏衣服洗一洗。
would be like trying to meet a friend in London without a pre-arranged rendezvous and absurdly wandering the streets in the hope of a chance encounter.