og-39

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（C）

(E) to protect

Choice C is best because the participle protecting begins a phrase that explains what the shields did. Choices A and B awkwardly use the singular word method to refer to items of military equipment rather than to the use of such items. Also, a method of protecting would be more idiomatic than a method to protect in A or a method protecting in B. In B and D, as is incorrect; also, a protection in D has no noun for which it can logically substitute. Choice E is incomplete; used to protect would have been acceptable.

a method of protecting为什么可以，是什么用法？谢谢