几种容易混淆的时态比较(一）
ten years before he came to our school.
本句中 work 的工作状态延续了ten years，直到before he came to our school为止。
He ________( be ) ill for weeks when he asked for sick leave.
She told me she always_________( work in the countryside since she graduated from a college.
本句中 work in the countryside的工作状态自graduated from a college开始，一直延续至she told me的时候。
3.在一段情景连贯的文字中，先发生的事放在后面叙述时，要用过去完成时。
She felt helpless,not knowing what to do. Her husband _________( die ) and left her no money.
她觉得孤立无援，不知所措，她丈夫去世了，没留给她财产。
在本句中，she felt helpless发生在过去，而 die 则发生在felt helpless之前。
4.表示过去未实现的希望、计划、打算或原本的想法时用过去完成时。常用的动词有think,suppose,hope,want,expect,plan等。
I ____________(think) he had died.
我原以为他已死了。
They _________(want) to catch the first bus,but they didn't get up early enough.
他们本想赶头班车，但起得不够早。
5.在宾语从句中，所叙述之事虽发生于主动词之前，但从句中有一个确定的表示过去的时间状语时或叙述的是历史事实时，从句中时态用一般过去时。
The teacher said that Columbus ________(discover) America in 1492.
老师说哥伦布在1492年发现了美洲。
句中的discovered发生在said之前，但不用过去完成时had discovered。
6.叙述过去发生的一连串的动作或事件用and或but连接时，用一般过去时。
He ________(get) up, ________(dress) himself and then _________(go) downstairs to have breakfast.
他起身穿好衣服，然后就下楼吃早饭。
He ___________(buy) a volleyball but later _____(lose) it.
7.当主动词与宾语从句中谓语动词同时发生时，从句谓语动词用一般过去时或过去进行时。
He said he ________( know )several languages.
他说他懂好几门外语。
He was not sure what they _________( do ) at that time.