One Day,a Classmate with Whom You've Been Trying to Go

One day,a classmate with whom you've been trying to go out socially gives you her phone number on a napkin.You put the napkin in your pocket,planning to save the number in your phone later.Unfortunately,you forget to save the number and wash your jeans without taking out the napkin.Now all you can piece together of the phone number are the first six digits.If you go to the phone and dial the first six digits plus "0",then dial the first six digits plus "1",then dial the first six digits plus "2",etc.until you dial the correct number,you are solving the problem by

A) using heuristics.
B) rote.
C) trial and error.
D) insight.