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

the african society basically suffered the consequences of colonization and apartheid directly attacking the black people, first, during the colonialism and its main idea which which "white people" had better rights, affecting   them principally in the right to establish black people in their territories, access to quality education and health services and took away any civil right even to the black people to feel they have the same opportunities as the settlers.

why does the crew join ahab's quest without hesitation?