请教 大全 SEC6-17

loveathgs

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

这个ing 和 to do 应该怎么区分？这里表目的不应该to do么？而且不应该用同位语消除误解吗？

果汁软糖

这题的关键不是to do或者ing，是同位语的表达，逗号后面的是military equipment的同位语，所以不能用method，因为equipment不是一种method

loveathgs

没看懂。。。

有同位语的话不是更清晰吗？