You have to leave now----- you want to catch the early bus.A

答案是D 这是一个条件句 ,只不过条件后置了。意思是：如果你想赶上早班车的话,你现在就应该离开。而选项A so that 是引导结果状语从句的,在这里根本讲不通啊如果用so that 句子应该做一些调整 ,you must leave now so that you can catch the early bus。