Which fits the text correctly?
redwood trees can live for 2,000 years because the wood and bark contain
tannins that protect the trees from fungal infections, insect infestations,
and

a. being burned by fire
b. burning
c. fires that destroy other trees
d. forest fires

The items in your comma series are "fungal infections" and "insect infestations." to keep this sentence parallel, you have to pick the answer choice that matches this organization--an adjective followed by a noun. "forest fires" is the correct answer. the other answer choices break the parallel structure; choice A adds another verb, when the verb for the comma series is "protect"; choice B throws another verb in like choice A; choice C doesn't have the same adjective-noun structure. instead it has a noun, then follows with a more in depth explanation.