[問題]OG Q3

[kaori110]

3.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

参考答案B。

想請問一下
B選項中的sounding是因為跟“ such as defending…., acting….., and scouting …” 平行嗎
OG 的解釋感覺是 “ such as defending…., acting…and sounding…, and scouting….”
通常不是最後一個平行才加 “and” 嗎?
我覺得是　ａｃｔｉｎｇ　ａｓ　ｓｅｎｔｉｎｅｌｓ　ａｎｄ　（ａｃｔｉｎｇ　ａｓ）　ｓｏｕｎｄｉｎｇ　ａ　ｗａｒｎｉｎｇ。。。
想請問大家這樣對嗎？