关于句子中单根破折号的使用

liyiqin926

在manhattan中写道

Sometimes,a dash is preferred. For instance, you should use dashes to separate an appositive from an item in a list.

You canalso use the dash to restate or explain an earlier part of the sentence. Unlike the colon, the dash does not need to be immediatelypreceded by the part needing explanation.

也就是说单根破折号可以引出同位语 和 引出解释说明的部分。
可是卤煮有一个问题。

Q:在判断句子是否完整的时候，应该把 单根破折号 看做什么成分呢？ 是连词？好像不对。  还是忽略不计？

例子如下：Thesubstances that Gross studied are maternal messenger RNA’s—products of certainof the maternal genes.  这是一个正确的句子应该是看做引出同位语的作用。

还有另外一个例子是og上的一道
Some anthropologists believe that the genetic homogeneity evident in the world’s people is the result of a "population bottleneck" -----at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.

• Aat some time in the past our ancestors suffered an event, greatly reducing their numbers
• Bthat at some time in the past our ancestors suffered an event that greatly reduced their numbers
• Cthat some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
• Dsome time in the past our ancestors suffered an event from which their numbers were greatly reduced
• Esome time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,    这道题答案选B 那破折号在这里到底起什么作用呢？
  

跪求各位牛牛解答   -________-''

• 
  

xiaoshenshen

对于破折号，我一向都破罐子破摔地抱着“你爱咋样就咋样”的想法。

这题一开始错选A了，后来看了答案，很make sense。A里的greatly reducing看起来主语很像是our ancestors，有歧义。CDE 错的比较明显

我记得这题的答案里没有提到A里缺that，说明GMAT本身对于——的用法也是很放得开的。

liyiqin926

xiaoshenshen 发表于 2013-8-22 19:22
对于破折号，我一向都破罐子破摔地抱着“你爱咋样就咋样”的想法。

这题一开始错选A了，后来看了答案，很 ...

嗯。。我也发现了

alvlen

xiaoshenshen 发表于 2013-8-22 19:22
对于破折号，我一向都破罐子破摔地抱着“你爱咋样就咋样”的想法。

这题一开始错选A了，后来看了答案，很 ...

赞“破罐子破摔”