Puritan fanatics brought to civil and military affairs a coolness of judgment and mutability of purpose that some writers have though inconsistent with their religious zeal, but which was in fact a natural outgrowth of it.fficeffice" />

(A) but which was in fact a natural outgrowth of it

(B) but which were in fact a natural outgrowth of it

(C) but which were in fact natural outgrowths of it

(D) but it was in fact a natural outgrowth of them

(E) which was in fact a natural outgrowth of it 为什么选 C 阿？[em25]

句子主干为：Puritan fanatics brought to civil and military affairs a coolness of judgment and mutability of purpose
that some writers have though inconsistent with their religious zeal, but which were in fact natural outgrowths of it做定语修饰a coolness of judgment and mutability of purpose
其中that some writers have.....和but which were in fact....并列fficeffice" />

though, 在这里什么作用？fficeffice" />

ecsniffer is right. a few more points here:

1, this is REVERSE: bring A to B ---- here, it is 'bring to BA' because A is too long

2, the subject of A is ' a coolness of judgement and mutability of
purpose' which has 2 attributive clauses led by 'that 'and 'which'

3, 'though inconsistent' is 插入语, modifying the subject of A. Below is a sentence I forged according to this one:
It is
fear that brings to our lives motivation that though not preferred we need to
move forward, and which actually becomes a driving force towards our
achievements.fficeffice" />