关于OG12-30 的E选项，请NN解答

wanghenan0431

30. 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

选择C没有问题，但是OG中队E的解释有些不明白“Although the infinitive to protect would work if it were not preceded by a comma, it cannot act as a nonrestrictive adjectival
phrase modifying items.”，意思是说就算前面没有逗号， to protect也不能做items的非限制性形容短语？  


不明白哦，请NN们解答， 多谢！

rainbowmanutd

http://forum.chasedream.com/GMAT_SC/thread-429359-1-1.html?SearchText=og12%2030