为啥选D,是虚拟语气主句和从句时态的问题吗,请说详细一点,

题目

为啥选D,是虚拟语气主句和从句时态的问题吗,请说详细一点,
____ the expense,I ____ a round-the-world tour.   A.Were it not … would take     B.If it were not… take   C.Weren't it for… will take      D.If it hadn't been for… would have taken

答案

虚拟语气的问题
在非真实条件状语从句中
　　1.表示与现在事实相反的情况
　　If I were ten years younger,I would travel round the world.如果我年轻十岁,我就去环球旅行.
　　2.表示与过去事实相反的情况
　　If the traffic hadn’t been so heavy,I could have been back by seven o’clock.如果交通没有那么堵的话,在七点钟以前我就回来了.
　　3.表示与将来事实相反的情况
　　If it rained / were to rain / should rain tomorrow,the crops would be saved.如果明天下雨,庄稼就得救了.(最近天气很好,明天根本不会下雨)