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hiiamjo

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（B）

(E) to act as a sentinel sounding

句子的结构是怎样的？ sentinels,sounding分别和什么构成并列？

vagrant

句子主体是：Some bat caves have residents that take on different duties。

后面的都是duties. sentinels不和谁构成并列吧，sounding 和defending, acting, scouting并列

hiiamjo

但是如果sounding,和defending,acting,scouting构成并列

就会出现，defending, acting and sounding, and scouting的句势，不是有问题么？