上网查了下，这两道题的答案有争议，求教NN们给个可以信服的正确答案
1
When an active tooth in the shark’s jaws is lost or worn down, many spare teeth lie in seemingly limitless reserve, each of which are ready to slide into the appropriate position.

A.
When an active tooth in the shark’s jaws is lost or worn down, many spare teeth lie in seemingly limitless reserve, each of which are ready to slide into the appropriate position.

B.
Whenever an active tooth is lost or worn down, many spare teeth lie in seemingly limitless reserve in the shark’s jaws, which are each ready to slide into the appropriate position.

C.
Many spare teeth lie in seemingly limitless reserve in the shark’s jaws, each one of which are ready to slide into the appropriate position when an active tooth is lost or worn down.

D.
The many spare teeth lying in seemingly limitless reserve in the shark’s jaws, each one of which is ready to slide into the appropriate position whenever an active tooth is lost or worn down.

E.
In the shark’s jaws, many spare teeth lie in seemingly limitless reserve, each one ready to slide into the appropriate position whenever an active tooth is lost or worn down.

答案给的是A，我选E，A中，each of which难道不应该跟单数吗？

2.

The Acoma and Hopi are probably the two oldest surviving Pueblo communities, both dating back at least a thousand years.

A.
both dating

B.
both of which have dated

C.
and each has dated

D.
and each one dating

E.
each one of which date

这道题的答案也有A和E 两个说法，我选A，E的错误我觉得跟上一道题是一样的啊。

自己先顶一下，请NN帮帮忙，多谢多谢

还是没有人回复，再顶一下，不要沉掉，多谢多谢

不要沉掉了，GWD题，请NN帮忙

这是哪里找来的题目？两个答案都错了！！！！！！！楼主选得正确。Each 是单数的。

现在有些政治正确意识浓厚的人，在 each 或 every 用来指代人时后面用 they。这是为了避免用 he 来代替一般的人。这是英语的缺陷，用 they 只是权宜。

在不指代人时，each 和 every 掌管的动词绝对不应该用复数。

多谢Asrgbf，都是GWD的题目，我也觉得答案不对，可是GWD给的答案和好多人写的JJ都是那个错的答案，搞得我confuse了半天，有Asrgbf确认放心了

GWD答案正确,　应该是A和E
第一题
　 　在gmat考试中百分比结构＋名词结构的系动词有名词本身来决定.　
如most, one third, minority,majority,each+名词时注意要看名词是不是可数.　如果可数用复数,不可数用复数
在这道题里each of which are , each 指的是teech,teech是可数名词固然用are 所以没错　
至于其他选项BDE有whenever 所以就错.因为它改变了原文的含义:
　　文章说当When an active tooth in the shark’s jaws is lost or worn down,时候会怎么怎么样,它们说无论如何都怎么样所以与原文含义冲突!所以不选.　
C选项与文章相比有很大变化,文章说When an active tooth in the shark’s jaws is lost or worn down  只有这样时spare teeth　会补全空位,强调的是前者,但C选项强调的是后者所以错.

注意:GMAT　SC追求的是简洁精炼,答案一般是对文章的最小改动,意思不能颠倒.

第二题
　其实A本身没有错误,但是GMAT考试里有这样一个规则:　动词>形容词>抽象名词>动名词　(　>意思是优于　)
在A和E的选项中前者用了动名词形式dangting,后者用了动词形式date 所以动词优于动名词原理选E,并且each one of which date里each指的是Acoma 或Hopi所以没错.
其他选项B  both of which 没有这样说法,C和D 有and 所以要求平行并列,但是前面没有这样的结构所以错.

第一题：GWD 的解释不对。这里和一个大群里面的部份没有任何关系。Each 指的就是一只牙齿，不论前面说的是几千几万，一用到 each 和 every 时就是指一个，必须是单数。

第二题：楼上说的什么优于什么的，根本没有这样的语法规则，GMAT 考试也没有这样的规定，只是某些人推断的结果，做不得准。因为 E 语法错误，所以根本不能选。至于
The Acoma and Hopi are probably the two oldest surviving Pueblo communities, both dating back at least a thousand years.
和
The Acoma and Hopi are probably the two oldest surviving Pueblo communities, each one of which dates back at least a thousand years.
那就两句都正确。

GMAT 这类题目，不要相信那些补习社提出来的规则，因为只是一些人的推论。其实我看过很多真题，答案都是非常明显的，同时错误选择都有语法错误或是句法错误，不会是与风格有关，不然就会被人告上法庭的了。