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正确答案是：B
【解析】：
这个句子考察了虚拟语气及其省略.
其实原句是这样的：If there were no gravity , there would be no air around the earth.
将If省略了,再将 were 提前.
虚拟语气里面只有 were ,没有 was,所以A 的was 改为were就对了.
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