For members of the seventeenth-century Ashanti nation in Africa, animal-hide shields with wooden frames were essential items of military equipment, a method to protect warriors against enemy arrows and spears.

(A) a method to protect
(B) as a method protecting
(C) protecting
(D) as a protection of
(E) to protect

The answers is (C). I chose (E). Please help to understand why (C) is the correct answer.

We can't use an infinitive after the comma. Remember that an infinitive functions as a verb, but we're trying to introduce a modifying clause here to provide further information about the military equipment.

This is just one of those things you have to memorize, unfortunately, especially if you are not a native speaker.

Got it Stacey. I guess you are correct. It makes it more difficult if english is not one's first language.

Thanks
GMAT 2007