看了之前的帖子还是不明白，求指教！！！

richygogogo

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.
A. at some time in the past our ancestors suffered an event, greatly reducing their numbersB.that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C. that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D. some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E. some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,
有几个问题：1，破折号的用法，这里为什么一定要是人类学家believe that X-that Y中Y的内容，而不是对前面内容的解释说明？2，great reducing balabala为什么不能是our ancestors suffered an event的结果状语？comma，Ving不是既能表伴随状语又能表示结果状语吗？求大神指教！已晕。

VincentFSJ

并没有说一定要有that吧？破折号单纯表解释而已
reducing这里如果作结果状语怎么理解？ancestors reduced their numbers, 显然不是祖先导致自己数量减少或者ancestor suffered 减少number，而是这个event的发生导致number's reduction。 所以就算改也要用an event occured balabala to ancesters, reducing balabala

richygogogo

结果状语不是前面整句话所导致的结果吗？我理解的是“祖先遭受了重大事件”这整个一句话的内容导致了他们数量的减少,这么理解不对吗？大神指教！！