would rather +从句,表达一种与事实相反的假设和愿望.通常情况下,表达于现在和将来相反的假设,句子中用一般过去时态表达；表达与过去情况相反的假设,用过去完成时态（had done) 表达.
比如：i would rather you came tomorrow.（将来）
Her mother would rather she didn't go to college.(现在)
She would rather that we hadn't left yesterday.(过去)
在这个题里,用过去式表示对将来的虚拟.选C.