一般在从句中使用一般过去时,主句中使用过去完成时.例如: Lily had written some letters before she went out shopping. 有时,也可以在从句中用过去完成时,主句中用一般过去时,这样就可使描述更为生动.试比较: We got to the station before the train had left.火车尚未开动之前,我们就到了车站. We had got to the station before the train left.火车开出之前,我们就已经到了车站. before本身就能明确地表示时间的先后关系,故多数主从句均使用一般过去时,而无需使用过去完成时.例如: Many people left for home before the film ended.电影尚未放完,许多人就起身回家了.