Prep1-95：
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
我还是很怀疑这个 and so 的用法，之前大家说这里so是副词，但是如果so是副词就没有“所以”这层意思了，也就是没有表达出前一句和后一句的因果关系啊？
请NN指正！我非常之疑惑！ | 
