Which character trait does the characterization from the passage above reveal about the grandfather?

a. frustrated
b. polite
c. serious
d. stubborn

my grandfather, who lost his short-term memory sometime during the first eisenhower administration, calls me into his study because he wants to tell me the story he’s never told anybody before again. .

my grandfather slams the door and motions me to the chair in front of his desk. i’ll be thirteen in two weeks. “there’s something i want to tell you, son,” he says. “something i’ve never told anybody. you think you’re ready? you think you’ve got the gumption? ”

“i think so.”

“think so? ”

“i know so, sir. i know i’ve got the gumption.” . .

“it was late,” he says. “someone knocked on my stateroom door. i leaped up. in those days i slept in uniform—shoes, too.” my grandfather smiles. his face is so perfectly round that his smile looks like a gash in a basketball. i smile back.

“don’t smile,” he says. “just because i’m smiling, don’t assume i couldn’t kill you right now. know that about a man.”

excerpt from "the raft"