Of ail the vast tides of migration that have swept through history, maybe none is more concentrated as the wave that brought 12 million immigrants onto American shores in little more than three decades.
(A) maybe none is more concentrated as
(B) it may be that none is more concentrated as
(C) perhaps it is none that is more concentrated than
(D) maybe it is none that was more concentrated than
(E) perhaps none was more concentrated than
OG的解释里说C选项的it must refer to something，这里it is that 不是强调句吗？为什么和it is clear that不一样呢？
还有 none is more concentrated中is的时态为什么要用过去时要跟brought一致呢，它是一个现象，是一个事实的话不是可以用一般现在时吗？跟第一句中的have swept一样。求解答啊，跪谢了！！作者: chenlencu 时间: 2013-2-18 19:03
好像og特别不喜欢用it is ...that...这样的句子。常常被判为awkward and redundant。
至于为啥是was，我觉得这个整个句子都在讲历史，through history.
more...than...这个也不须多说。所以我觉得应该选E。作者: mslancaster 时间: 2013-2-19 21:09
（1）強調句的it，是不指代任何內容的...lz可以百度一下強調句的語法。
it有指代用途的只能是形式主語/賓語，還有就是普通指代（跟they它們用法一樣）
it is clear that...，這裡it是做形式主語，指代的是that-clause，但是，這一個並不是強調句...
不是所有的it is...that..都是強調句的。
（2）【from Ron】
if you are directly describing historical events, you have to use a verb tense that can properly refer to past events. (by “directly” i mean as opposed to, say, discussing the implications of historical events on the present, or evaluating them from a present-day standpoint. in those kinds of contexts, the present tense could be quite reasonable.)
have swept強調的是vast tides已經發生了，它們的發生對現在仍然存在影響作者: Seven9208 时间: 2013-2-20 06:46
