紧急:请教一道语法题

请教：mountain yellow-legged frogs 这道语法题，觉得答案应该是C吧，能解释一下为什么是E吗？E里面So本身也是连词，使用And so是不是太累赘了

Unlike frogs that metamorphose from tadpoles into adults within a one-year period, it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are restricted to deeper bodies of water that do not dry up in summer or freeze solid in winter. 
(A) it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are

(B) it takes the mountain yellow-legged frog of the Sierra Nevada three to four years until it reaches adulthood, and therefore it is

(C) in the Sierra Nevada, mountain yellow-legged tree frogs take three to four years to reach adulthood, thus being

(D) mountain yellow-legged frogs of the Sierra Nevada take three to four years until they reach adulthood, thus

(E) mountain yellow-legged frogs of the Sierra Nevada take three to four years to reach adulthood, and so they are

用UNLIKE排除,只剩D,E了.而E用TO REACH ADULTHOOD明显简洁.且D的THUS后无主语

继续请教

1. Unlike不能排除C吧? C的主语也是mountain yellow-legged tree frogs, "in the Sierra Nevada" 可以看作修饰主语的定语.

2. C中thus的用法也是对的

3. E中"and so"如果看作一个词，则是个副词，表示"因此", 那么句子缺连词，不完整；如果把and和so都看作连词，则两个连词连用--累赘。

mountain yellow-legged frog of the Sierra Nevada 不可写成in the Sierra Nevada, mountain yellow-legged tree frogs .第一，unlike要求意思和结构都对等，也就是说第一个逗号后一定要跟比较对象，跟个地点状造成不平衡，所以说不符合UNLIKE用法。而且GMAT语法里，尽量别选把限定成份单独拿出来做个状语的选项，对作者原本所强调的词语意思有改变。

还有，C选项里逗号后接thus搞到后半句无主语已经错了，加个being想弄个伴随状就更不对了。

so是副词当然加and才能连句子；

they是后半句的主语。

建议楼主弄清时间地点状语，定语从句和并列结构等语法概念。

建议楼主复习unlike,whereas,as be the case 等比较结构的使用方法。

建议楼主参看PREP SC