现在分词前面有逗号时，到底修饰什么

OG12 第30题

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
Logical predication; Rhetorical construction
Th e underlined part of the sentence begins a
phrase describing items of military equipment. It is
awkward and inaccurate to describe items
themselves as a method. Replacing the underlined
phrase with the participle protecting creates a
modifying phrase that clearly explains the
purpose of the items of military equipment.

按ETS的解释，protecting是修饰items of  military equipent

但是现在分词前面有逗号的时候，不是一般都修饰前面的主语和谓语吗？为什么在这里是修饰就近的表语名词呢？