请问这句话的语法分析,虚拟语气与倒装
The Achievements of the greatest minds in science could never have been reached had it not been for the patient work for hundreds of others.
1.请问句中为什么要用could?这是什么语法结构?
2.这句话中倒装和虚拟语气在哪里?
最后,这句话全句怎么翻译?