为什么选D ___no gravity,there would be no air around the eartha if there wasb was therec if there had been d were there
问题描述：
为什么选D
___no gravity,there would be no air around the earth
a if there was
b was there
c if there had been
d were there
答
这题是对虚拟语气的考察，用排除法。从整句来看，意思是：如果没有重力，地球上将不会有空气。明显的是虚拟语气，因此可以排除AB，因为虚拟句里，比动词要用were。而排除C的原因则是因为整个句子并不是完成的关系。
答
假设没有重力，是虚拟语态，there were
if条件状语从句的虚拟语气
一般有were/had done/should do
if省略，谓语提前
所以是were there
答
此题考察虚拟语气的用法.因为不可能没有重力,所以用虚拟语气.现在虚拟语气be动词一律用were,所以a b错误,c 应为if there were,if there had been 为对过去虚拟也不对.were there为if there were的省略倒装形式,故选d 具体虚拟语气的用法可以参考语法书.
答
虚拟语气，省略了IF