问题
单项选择题
The achievements of the greatest minds in science could never have been reached if it had not been for the patient and accurate work of hundreds of other people.
A．has it not been
B．if it had been
C．if hasn't been
D．had it not been
答案
参考答案：D
解析：结构应用。此句是虚拟语气用法。虚拟语气中含有if条件句，主语又为it时，应省略if，句子倒装；又因此句表达的是与过去事实相反的假设，应用过去完成时，所以选项D正确。