XDF补充, section 6, No. 17

17. 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

answer is e)

i wonder why c) is not good as e) is that protecting is ambiguous because of  'for numbers'...??

你这是哪里来的题和答案？

这题是OG39，答案是C.