请教PREP1 165

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Due to poaching and increased cultivation in their native habitats, researchers have determined that there are fewer than 100 Arabian leopards left in the wild, and that these leopards are thus many times as rare as
            China's giant pandas.

(A) Due to poaching and increased cultivation in their native habitats, researchers have determined that there are fewer than 100 Arabian leopards left in the wild, and that these leopards are thus many times as rare as

(B) Due to poaching and increased cultivation in their native habitats, there are fewer than 100 Arabian leopards left in the wild, researchers have determined, making them many times more rare than

(C) There are fewer than 100 Arabian leopards left in the wild due to poaching and increased cultivation in their native habitats, researchers have determined, which makes the leopards many times more rare compared to

(D) Researchers have determined that, because of being poached and increased cultivation in their native habitats, there are fewer than 100 Arabian leopards left in the wild, thus making them many more times as rare as

(E) Researchers have determined that, because of poaching and increased cultivation in their native habitats, there are fewer than 100 Arabian leopards left in the wild, and that these leopards are thus many times more rare than

这道题目做过了三次都错了，答案是E，可是我想问一下their的指代不会有问题吗？还有rare的比较级不应该是rarer吗？谢谢大家啦。

rarer
adj.
更稀罕的,更珍贵的（rare的最高级）

这是金山词霸上的解释。

their指代没有错误，because of引到的原因状语从句，修饰后面的there be句子，可以拿掉，跟主句researchers没有任何关系，自然不会修饰错误。

可以不考虑插入语的指代么? 好象只是说如果代词先于主句主语出现,则指代主句主语,但这里researcher已经出现了,还是会有影响把

rare的金山词霸解释：最高级是rarer

longman上：comparative rarer superlative rarest

但是google上很多more rare的例子：

MORE RARE BOOKS COMING TO AMERICA G.D. Smith the Biggest Buyer at the Sale of....

Google donates $3M to help scan more rare documents....

But there’s another type of breast cancer – much more rare and much more lethal ....

Earth-like planets may be more rare than thought : Nature News....