单选题 ______ no gravity, there would be no air around the earth, hence no life.
A. If there had been B. If there was
C. Had there been D. Were there

【正确答案】 D

【答案解析】[解析] 语法题目，考查的是虚拟语气。由题意，如果没有重力，表明一种假设情况，应用虚拟语气，即if there were no gravity。故正确答案是D选项，为省略了if的形式。