Jennifer: What’s the smell? The room smells like cigarette smoke.
Vicki: You’re right. My boss has just smoked here.
Jennifer: Open the window, please. I can’t stand the smell of the cigarettes. It makes me uncomfortable.
Vicki: Actually, it has been a year since Jay smoked. I don’t know why he’s been smoking recently.
Jennifer: Maybe he’s under a lot of pressure these days.
Vicki: Does your father smoke?
Jennifer: No, he doesn’t.
Vicki: It is ten years since my father began to smoke.
Jennifer: You should persuade him to give up smoking. It’s harmful.
Vicki: I tried, but it didn’t work.
Molly: Kathy，对话里有两句话很相似，它们表达的意思相同吗？
It has been a year since Jay smoked.
It is ten years since my father began to smoke.
老师：你觉得呢，Molly？
Molly：我觉得都是表达“已经抽烟多少年”的意思。
老师：这么看来，关于“It is/ has been +时间段 + since + 从句”的这个结构和用法你还不清楚哦~
Molly：那老师给我讲讲吧！
老师：这个句型所表达的含义要视since从句的谓语动词而定，
（1）若从句谓语动词为瞬间性动词，表达肯定意义，表示“自从从句中的动作发生以后，时间已经过了多久”。
如：
It is two years since Jim came to China.
Jim来中国两年了。
It has been three years since they got married.
他们结婚已经三年了。
Molly：知道了，老师。
老师：
（2）若从句谓语动词为延续性动词，则表达否定意义，表示“自从从句的动作结束以来，时间已经过了多久”。
如：
It is/has been ten years since he was a doctor.
此句中的系表结构（was a doctor）表示一种状态，这种状态是延续的，表示否定意义，译为“不是，不当”，故这句话的意思是“他不当医生已经十年了。”
Molly：哦~我明白了。
老师：试比较课堂前的两个句子：
It has been a year since Jay smoked.
It is ten years since my father began to smoke.
Molly，你现在可以区别出两句话的差异了吗？
Molly：嗯！前一句的意思是“Jay戒烟已经一年了。”，后一句的意思是“我爸爸抽烟已经十年了。”
老师：Good！smoke是延续性动词，所以在句中表达否定含义，要译作“戒烟”而不是“抽烟”；begin是瞬间性动词，在句中表达肯定意义，直译即可。
Molly：I got it!
老师：注意，在此句型中，since从句的谓语动词要使用一般过去时且不能用否定式来表达否定意义哦~
例如表达“他好久没学汉语了。”
我们不可以说：
（误）It is a long time since he didn’t study Chinese.
而是要说：
（正）It is a long time since he studied Chinese.
Molly：知道啦！
老师：A miss is as good as a mile. 失之毫厘，谬以千里。这个句型中，从句谓语动词是否为延续性动词至关重要哦~