We believe that if animals ran the labs, they would test us to determine the limits of our patience, out faithfulness, our memory for locations.
我们认为如果动物掌管实验室的话，它们会对我们进行测试，以确定我们的忍耐度、忠诚度以及方位记忆力。
1）表示与现在事实相反时，从句的谓语动词用一般过去时，主句的谓语动词用would/could/should/might+动词原形
如：If I were you, I would tell her the truth.
2）表示与过去的事实相反，从句的谓语动词用过去完成时，主句的谓语动词用would/could/should/might+have done
如：If you had come here yesterday, you would have see him.
3）表示与对将来的主观推断时，从句谓语动词有三种形式：should+动词原形，were+动词不定式，一般过去时，
主句的谓语动词用would/could/should/might+动词原形
如：If it should snow tomorrow/If it were to snow tomorrow/If it snowed tomorrow, many crops would die of cold.
当虚拟条件句的谓语动词含有were，should，had时，if可省略，将were，should，had等词置于句首（即除了were+动词不定式的条件状语都可以倒装）
Were I you, I would tell her the truth.（与现在事实相反）
Had you come here yesterday, you would have see him.（与过去事实相反）
Should it snow tomorrow, many crops would die of cold.（对将来的主观推断）