7. I had written my composition before the bell rang.
【过去完成时】表示在过去某个时间之前发生的动作。关于“过去完成时”，有不少同学认为它是指“过去完成的动作”，这是非常错误的理解。通俗一点解释就是：两个动作都发生在过去，较早的那个动作用过去完成时，另一个用一般过去式。它的实质就是“过去的过去”。
【构成】had +过去分词(动词-ed)
【常用的时间短语】by the time…, by the end of等。例如：
The train had left by the time we got to the station.
He had learned 3000 English by the end of last term.
The children ran away because they had broken the window.
Tom was disappointed that most of the guests had left when he arrived at the party.
He told me that he had broken his glasses.
【注意】当两个动作先后分明，谁先谁后一眼就看出来时，在先的那个动作则不必用过去完成时，如：
He came in and sat down, and then took out his pen.
或者有after, before时，如：
After we said goodbye to them, we left the village. 我们向他们道别后，离开了村庄。
I heard a sudden cry just before I turned off the light. 就在我熄灯前，我听到突如其来的一声叫喊。