【问】“Why do you drink so much coffee?”
 “Well._______it doesn't keep me awake nights，I see no harm in it.”
 A. although B. as long as
 C. as far as D. for(TOEFL，74. 6)
 答案规定只能选B，而不能选C。这是为什么呢?
 【答】 as long as用作连词时，其主要意思是“只要”，而as far as是指“在……范围内”，引导限制状语从句，常常用于下列结构：as far as I know(据我所知)，as far as I can see(据我看)，asfar as I'm concerned(依我看，就我而言)。
 请对比下面的例句：
 1. I'm happy as long as you are happy.(Greene)
 只要你幸福，我就感到幸福了。
 2. As long as you can keep away from them you’re safe. (Mansfield)
 只要你脱离他们，你就安全了。
 3. There's only one thing to be done，as far as I can see. (Dreiser)
 据我看，只有一件事需要做。
 4. Man： Will the field trip be on Friday as originally scheduled?
 Woman： As far as I know. (TOEFL，85.5)
 男：郊游还是象开始计划的那样星期五去吗?
 女：据我所知，是这样的。
 5. I will help you as far as I can.
 我将尽力来帮助你。
 6. He will help you as far as possible(as far as lies in his power). (ALD)
 他会尽力帮助你的。
 7. As far as prescience allows us to tell，Russia has a unique ability to cause trouble. Chinaand India，says a senior official，“don’t have 30000 nukes... Russia has too much of ahistory of being a major global power to be ignored.”(TIME)
 在我们能预见的范围内，那就是它有一种独特的制造麻烦的能力。中国和印度没有3万件核武器……而俄罗斯作为全球大国的历史太久，因而不能忽视它。(时代周刊)(转引自《现代英语报刊阅读词典》)
 as far as还有其他用法：
 A.“一直到……”，既可表示实际距离(行程长度)，也可用于比喻性的距离：
 1. “No，30th Street is____.”
 A. the farther the bus will go B. as far as the bus goes
 C. only as far as the bus is going D. far as the bus is going(TOEFL，73. 3)
 2. I walked as far as the church. (Hemingway)
 我一直走到教堂。
 3. Yes，we walked as far as the river. (LDAE)
 是的，我们一直走到河边。
 4. Yesterday we went as for as the third line on page 20.
 昨天我们已看到第20页第3行。
 B.像……那么远
 We didn’t go as far as the others(did).
 我们没有像其余的人那样走那么远。