In "The Adventure of the Blue Carbuncle," which best describes Dr. Watson?
a. a wealthy man who loses a very valuable item to a cunning thief
b. a plumber who has been convicted of robbery before but who is innocent in this case
c. a logical and intelligent person who is impressed by Sherlock Holmes's powers of deduction
d. a poor man who tries to do something nice for his wife, but ends up being robbed