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题库 / GMATLA-SC-94
In the 1820's, anthracite coalfields opened in eastern Pennsylvania, and when canals and eventually railroads reached into the region, there were substantial supplies of coal that was exported to the nation's growing mills, forges, factories, and railways.
when canals and eventually railroads reached into the region, there were substantial supplies of coal that was
once canals and eventually railroads reaching into the region, there were substantial supplies of coal having been
with canals and eventually railroads reaching into the region, there had been substantial supplies of coal
canals and eventually railroads reached into the region, with substantial supplies of coal being
as canals and eventually railroads reached into the region, substantial supplies of coal were
题目分析：本题的意思是：
当运河和铁路到达地点时，很多的煤炭会被运输出去。
选项分析：
选项A：本选项语法没有问题，但是when连接的两个句子之间不存在时间关系。主句there were substantial supplies of coal是there be句型，其核心词为“有”。在逻辑上， 我们不能说：
当运河和铁路到达地点时，这里有很多的煤。
这是因为，无论运河到不到达这个局域，这个区域中的煤都是一直存在的。
选项B：两句话之间没有逻辑关系错误同选项(A)。分词短语having been不正确。在现在分词或不定式中加have表示先时性。到本选项中，其表示，在“有”足够的煤之前，煤就已经被运出去了，这显然是不符合逻辑的。
选项C：两句话之间没有逻辑关系错误同选项(A)。
选项D：本选项中的主句为canals and eventually railroads reached into the region。在划线部分身前出现的句子是anthracite coalfields opened in eastern Pennsylvania。这两句话没有并列关系。在逻辑上，是“煤矿被开采”和“煤矿被输出”之间形成并列关系。
选项E：Correct. 本选项在语法和逻辑上均是正确的。
Mark下，只能说是中英语义问题，根据答案那么确实有supplies of coal were exported的表达，只能靠平时积累，记下来吧。。。(同栽……)这个题还是从大语义上判断，明显e比there be意思更顺也更平行∥些，比如and前后都是主谓结构，无倒装。
(只能说尽量不要选there be 吧，GMAT不喜欢这个句型，大概率事件，且还出现在划线部分。。。)
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选项B once后面缺动词
选项C had been时态错误
选项D being多余；with substantial部分变成伴随，改变句子重心
选项E 正确
E.是原因状语，加主句
通过分析成分，显然canals and eventually railroads reached into the region与substantial supplies of coal were exported两件事直接因果关系更强，所以E优选，而且helr的分析里面也说了A中there be的错误
别扯淡了 都是绝对错误 还没有区别登录 或 注册 后可以参加讨论
E. as canals and eventually railroads reached into the region, substantial supplies of coal were-" 'as canals...' presents a reason as of why the substantial supplies of coal were exported."-CORRECT.
D is typical wrong answer which is grammatical but contains meaning problem. absolute phrase modifying wrongly the main clause is the favorite of gmat. this situation happen often in og and gmatprep.