Sentence Correction

Please explain the answer with reason and why are other choices wrong .. i realllyyy need to understand the difference

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
(E) to protect

C. Protecting...as there is a need of participle....to connect the two part of sentences...and to maintain the flow of sentences.