7、Corporation2、IftheHousesofParliamenthadnotbeenburneddownin1834,thegreatclockwouldneverhavebeenerected.if引导的非真实条件句,表示对过去事实的虚拟。对过去事情的虚拟:if+从句(过去完成时),主句(wouldhavedone)e.g.要是我在学校时再努力一点,我现在就会有一个更好的工作了。对现在事情的虚拟:if+从句(一般过去时),主句(woulddo)e.g.如果我是你,我就努力工作。If I were you, I would w