Unit 10 By the time I got outside,the bus had already left.
1. When I got to school, I realized I had left my backpack at home. (P76)我到学校时才发现把书包落在家了。
(1)had left my backpack at home 这是一个过去完成时的句子，表示在过去某一时间或某一动作之前完成的动作或存在的状态。
By three o’clock yesterday afternoon we had finished the work.
She had learned a lot of English before she went to school.
Li Min left his dictionary in the reading-room yesterday.
I have forgotten the book. 我忘记拿书了。
2. My alarm clock didn’t go off, and by the time I woke up, my father had already gone into the bathroom and I had to wait for him to come out. (P78)我的闹钟坏了，因此等我醒来的时候，我父亲已经进去洗澡了，我只好等他出来。
(1)go off 是“（闹钟）闹响”的意思，即“发出声音”。
The thieves ran away when the burglar alarm went off.
(2)by the time I woke up 中的by the time意为“到……的时候”。
By the time he was ten, Tom built a chemistry lab himself.
3. I started walking, but I knew I couldn’t get to school on time. (P78)我开始步行，但我知道我已经不能按时到达学校了。
(1)start to do sth和start doing sth都表示“开始做某事”，常可相互替换。
At the age of 12, he started writing his own newspaper.
= At the age of 12, he started to write his own newspaper.
Li Ming’s father seldom goes work on time. 李明的父亲很少准时上班。
The party began on time that evening. 晚会在那天下午准时举行。
How many times did you see the movie? 那部电影你看了几遍？
I have four times as many books as you.我的书是你的4倍。
I will try my best to finish it in time. 我会尽力及时完成。