as as 的用法It is ---- it is long.A.half not as wide as B.wide not as half as C.not half as wide as D.as wide as not half

　　选c
　　一般not紧跟在be动词后.
　　as...as意为"和……一样",表示同级的比较.使用时要注意第一个as为副词,第二个as为连词.其基本结构为：as+ adj./ adv.+as.例如：
　　(1)This film is as interesting as that one.这部电影和那部电影一样有趣.
　　(2)Your pen writes as smoothly as mine.你的钢笔书写起来和我的一样流畅.
　　其否定式为not as/so +adj./ adv.+as.例如：
　　This dictionary is not as/so useful as you think.这本字典不如你想象的那样有用.
　　若有修饰成分,如twice,three times,half,a quarter等,则须置于第一个as之前.例如：
　　Your bag is twice as expensive as mine.你的袋子比我的贵一倍.
　　几个关于as...as的常见句型：
　　(1)as...as possible
　　Please answer my question as soon as possible.请尽快回答我的问题.
　　(2)as...as usual/before
　　She looks as pretty as before.她看起来和以前一样漂亮.
　　(3)as long as...(引导条件状语从句)
　　It took us as long as three years to carry out the plan.我们花了长达三年的时间才完成这项计划.
　　(4)as far as
　　He walked as far as the railway station yesterday evening.昨天傍晚,他一直散步到火车站.
　　(5)as well as
　　She cooks as well as her mother does.她烧菜烧得跟她母亲一样好.
　　一些带有as...as结构的常见短语归纳：
　　as busy as a bee像蜜蜂一样忙碌
　　as easy as ABC像ABC一样容易
　　as deep as a well像井一样深
　　as light as a feather像羽毛一样轻
　　as soft as butter像黄油一样软
　　as rich as a Jew像犹太人一样富裕