关于连词连用的问题（第一次提问，倍儿紧张...）

lsydoudou

语法笔记上有这么一道题：
The particular design of muscles and bones in the neck and limbs of the turtle allow that it can draw
in its exposed parts such that an attacker can find nothing but hard shell to bite.

(A) allow that it can draw in its exposed parts such that
(B) allow it to draw in its exposed parts, and so
(C) allows for it to draw in its exposed parts and that
(D) allows that it can draw in its exposed parts, and so
(E) allows it to draw in its exposed parts, so that

B的解释是：allow应该用第三人称形式；and与so都是连词，重复。


但是后来有出现这样一道题：
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

正确答案是E
那连词到底能不能连用呢？
求解答……真的很迷惑……

lsydoudou

为什么木有大侠来伸出援手……