1. It is some time(一段时间) + since引导的时间状语从句= It has been some time(一段时间) + since引导的时间状语从句该固定句型意思是“自从.以来已经多久时间了”。2. 其中要求since引导的从句必须采用一般过去时，而主句是一般现在时或现在完成时。3. 补充：该从句的谓语动词是瞬间性动词时，从句正常翻译；而如果该从句的谓语动词是延续性动词作，从句必须作否定翻译。如：It is two hours since he left the classroom.自从他离开教室以来，已经两个小时了。It is three years since he worked there.自从他不在那儿工作以来，已经三年了。例句：1. It is / has been four days since I caught a cold. 我感冒已四天了。2. It is / has been two weeks since we met last. 自从我们上次见面以来已过了两周。我们会发现“It is +段时间since.句型”在翻译成中文时，有绝然相反的两种意思，一是，“。做。有多长时间了。”另一是“。有多长时间没做。了。”怎样以简洁的讲解让学生明了。我的意思是：先让比较两个句子的意思（中英文对照）。如， It is five years since he became a soldier.他当兵已经五年了。 It is five years since he was a soldier.他不当兵已经五年了。再如， It is two weeks since he fell ill .他病了两星期了。 It is two weeks since he was ill. 他病愈两星期了。让学生观察since 从句中动词的特点吧。第一种情况的动词是短暂性动词。表示从这点开始。而第二种则是状态性的，可延续的。练一练： 1. He went abroad in 1997 and has never come back. It is eleven years since he _the company at home.A. takes charge of B. took charge of C. is in charge of D. was in charge of*答案选D不选B2.They asked me to have a drink with them.I said it was nine years since I_a good drink. A.enjoyed B. was enjoying C. had enjoyed D. had been enjoying* 答案用 C 3.This is really a splendid evening. Its years _I enjoyed myself so much.A. when B. that C before D .since