英语翻译那为什么用were不用was?

英语翻译那为什么用were不用was? If today were the last day.那句话中为什么用were,而不用was.求高人指点 how was their holiday 为什么用was而不用were 为什么用he were而不用he was? If I were a boy中,为什么要用were不用was? there were no more mountains in sight.为什么用were 不用was If I were a bird的英语语法问题?为什么用were 不用was? I thought you were be taller.这里为什么不用was,而用were? Susan is walking slowly as if she were tired问:为什么用were而不用was if I were a boy为什么要用were不用was?求解 为什么If only I were abird.中的were不用was 为什么 if i were a boy 中的were 不用was?