Sentence Correction

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

OA C

Can anybody please explain the answer ?[/spoiler]

The underlined portion of the sentence should modify "equipment" and equipment cannot be "a method to protect". Hence A, B and E are out.

D is absurd - equipment cannot be - "as a protection of"

Hence C is correct.

Hope this helps.

why E is wrong ?

How do we know whether to use a gerund or an infinitive ?

Please explain.

"protecting" creates a modifying phrase that explains the purpose of "equipment". The infinitive 'to protect' is an adjective modifying "items" instead of "equipment".

hence the -ing form of the verb is needed.

Hope that helps.