Sentence Correction

Some bat caves, like honeybee caves, 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 sentinel sounding


[spoiler]IMO D; OA Later.[/spoiler]

My approach is:

Some bat caves, like honeybee caves, have residents that take on different duties such as [Idiom - such as X and Y] 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.

I am treating acting as sentinels and to sound as a subordinate clause because all options include an 'and' and the non underlined portion also has and. Since, there can be only one and used in a list separated by commas, I felt to act as sentinels and to sound must be parallel to each other.

Please suggest your opinion guys.