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2．I developed very slowly and it took nearly two hundred years before I was built as an analytical machine by Charles Babbage. 我发展很慢，差不多到了两百年之后，查尔斯·巴比奇才将我制成了一台分析机。 句型提炼： before引导的时间状语从句 (1)“It took＋一段时间＋before＋从句(一般过去时)”句型，表示“过了一段时间后才……”。该句型中的主句谓语动词多使用be动词。 (2)It will (not) be＋时间段＋before＋从句(现在时)表示“要过一段时间后才……(用不了一段时间就……)”。 【句型剖析】 (3)It was (not) ＋时间段＋before＋从句(过去时)表示“过了一段时间后才……(没过一段时间就……)”。 (4)It is/has been＋时间段＋since＋一般过去时，表示“自从……已多长时间了”。 (5)It was＋时间段＋since(从句用过去完成时) 表示“自从……已多长时间了”。 It was three weeks before the problem was solved. 过了三周问题才得到了解决。 The young man rushed out before I could tell him the news. 我还没来得及告诉他这个消息，这个年轻人就冲了出去。 It has been three months years since I applied for the job. 我申请这份工作已经三个月了。 【即时巩固】 语法填空 ①It took about four months ____________ the explorer found the new land. ②It will be long before he ____________ (master) all the advanced technology. ③It is six years ____________such deadly diseases arose. 【答案】①before ②masters ③since | 
