What's the difference between periodically vs. routine?

He said it was because a private detective sees the dark side of human nature. but whatever the reason, gill landers had an innate suspicion of politicians. when senator randy brill walked into his office on that summer day in august, mopping his flushed features with a monogrammed handkerchief, gill could think of no good reason to change his attitude. he'd only met brill once. that had been two years ago at a country club reception for state political notables. since then, he'd learned all he wanted to know about the senator's sinister reputation. gill sat back in his chair, put his feet on his desk, and fought to keep a poker face. but there was no way he could stop the chill that coursed along his spine like a rush of ice water. 29. in this paragraph, the word notables probably signifies that the persons so described a. would like to be politicians. b. are wealthy people. c. have political influence. d. are contributors to charity.