OG Verbal SC#2:原来"and"还能这么用？

siriushe

Some bat caves, like honeybee hives, have residents that take on different duties such as defending the entrance, acting as sentinels and to sound a warning at the approach of danger, and scouting outside the cave for new food and roosting sites.

(A) acting as sentinels and to sound

(B) acting as sentinels and sounding

(C) to act as sentinels and sound

(D) to act as sentinels and to sound

(E) to act as a sentinel sounding

正确答案：B。
官方答案解释为四个现在分词需要平行。
我的疑问是：为什么scouting前已有and，而答案中acting和sounding之间还要加and呢？
后来在老外的论坛上找到了一种说法：
因为后面没有划线的部分已经用了两个and(and scouting和and roosting)，所以可以由此推测出GMAC认为在本句中平行词语间用多个and是没有问题的！


想请教各位的是：这种用法是仅限于这一题还是属于通用的正确语法呢？

aeoluseros

主要是因为acting as sentinels and sounding a warning at the approach of danger是同属（放哨）一个意群才在中间加上and的，要不然是不可以随便加的。

siriushe

那后面“and scouting outside the cave for new food and roosting sites.”为什么也能加两个and呢？

wtx2490467

new food and roosting sites应该是一个意群, roosting是形容词修饰sites,是说栖息的地点,

dennis2k

这题虽然蒙对了，不过看了楼上的解释，学习了