In Which of the Following Would the Acquisition of a Classically

In which of the following would the acquisition of a classically conditioned response be the fastest?

A) Hugh rings a bell immediately after he gives his dog a treat.
B) Hugh rings a bell and then gives his dog a treat 30 minutes later.
C) Hugh rings a bell often, and gives the dog a treat after every fifth ring.
D) Hugh rings a bell and then immediately gives his dog a treat.