标题: 请教16 Verbal Review--SC#38 [打印本页] 作者: 阿鹿鹿鹿 时间: 2016-3-25 19:15 标题: 请教16 Verbal Review--SC#38 各位大大好~
想请教一下下面这题：
Around 1900, fishermen in the Chesapeake Bay area landed more than seventeen million pounds of shad in a single year, but by 1920, over-fishing and the proliferation of milldams and culverts that have blocked shad migrations up their spawning streams had reduced landings to less than four million pounds.
(A) that have blocked shad migrations up their spawning streams had reduced landings to less
(B) that blocked shad from migrating up their spawning streams had reduced landings to less
(C) that blocked shad from migrating up their spawning streams reduced landings to a lower amount
(D) having blocked shad from migrating up their spawning streams reduced landings to less
(E) having blocked shad migrations up their spawning streams had reduced landings to an amount lower
此题正确答案为B，我选的C。
当时做题时我虽然有看到By这个明显的标志词，但是由于题干里around1990年那句发生在前并用的是一般过去式，所以觉得后面by
1920那部分如果用了过去完成时不就是代表less thanfour million pounds发生在1900那个状况前了吗？
想问为什么B是对的呢？
谢谢谢谢~作者: 医生吃鱼 时间: 2016-3-25 20:27
该题C最明显的错误不是时态，而是reduce和to a lower amount语义重复。
关于过去完成时，你说得对，它有两种用法：
1、当句子里有两个过去的动作，过去完成时可以代表那个更早发生的动作。
例OG16-SC27：In the seventh century B.C., the Roman alphabet was adapted from the Etruscan alphabet, which in turn had been adapted in the previous century from a western Greek alphabet, which itself had been adapted earlier in the same century from the Phoenician alphabet.
2、表示动作在过去持续了一段时间。这就是该题的情况。
by 1920代表1900年到1920年这一段时间，因此可以用过去完成时。
PS：个人认为，GMAT中很多题目符合第2种情况时，过去完成时和一般过去时可以互换。 作者: 阿霖 时间: 2016-4-17 16:15
我想弱弱的问下 blocked shad from migrating up their spawning streams是什么意思呀？作者: lmx417139 时间: 2016-4-17 17:26
建议LZ看一下曼哈顿语法Guide8 P126上半页的解释，就是关于GMAT考点中past perfect verb的动词在句中不是作为最早出现的动作的情形。作者: yujieqiong 时间: 2018-1-20 10:49
这道题：
1.题目里的"by 1920"就是时间指示词，by+time或less than xx years later(从一个过去时间出发）都是GMAT很爱用的时间指示词。
2.by 1920到结尾是单独的independent clause，而had reduced是最早的行为（比较reduce和1920，blcok是that从句里的）
所以这里的had reduced没什么问题，不过这里用一般过去时我觉得也没啥问题，也不是一定要表达持续。