since 和 for 用法

Since 和 for 的用法 Since 和 for 的用法 示过去已经开始持续到现在的动作或状态常用的时间状语有：for, since, how long, so far, these days等。 Since+过去点的时间，for+一段时间（数词+量词），此划线部分用how long提问。 It is +一段时间+since…的句型与It has been +一段时间+since…意思相同。前者是说法，后者是口语说法 1) since +过去一个时间点　(如具体的年、月、日期、钟点、1980, last month, half past six)。 　 I have been here since 1989. 2) since +一段时间+ ago 　 I have been here since five months ago. 3) since +从句　 　 Great changes have taken place since you left. 　 Considerable time has elapsed since we have been here. 4) It is +一段时间+ since从句 　 It is two years since I became a postgraduate student. 　　一、since短语或从句表示过去的动作延续至今，since之后的时间为一点。 如： 　　Mr. Smith has worked here since 1984. 1984年以来，史密斯先生一直在这工作。 　　He’s learned about 5,000 English words since he went to college. 他上大学以来大约学了五千个。 　　二、for短语表示动作延续多长时间，for的宾语为时间段。 如： 　　We have known each other for twenty years. 我们认识有二十年了。 　　I haven’t seen her for a long time. 我好久没有见到她了