What is the part of speech of the underlined word in the sentence?

the rumbling thunder had startled my younger sister.

a.
noun

b.
adjective

c.
conjunction

d.
verb
had startled is underlined

What is the tone of the following passage from a river runs through it by norman maclean? “this was the last fish we were ever to see paul catch. my father and i talked about this moment several times later, and whatever our other feelings, we always felt it fitting that, when we saw him catch his last fish, we never saw the fish but only the artistry of the fisherman.”