Attempting to Encourage Employees to Improve Work Speed, Management at a Chain

Attempting to encourage employees to improve work speed, management at a chain of automobile repair shops offered bonuses to mechanics who bill more than $200 per hour. As a result, mechanics overcharged for simple repairs and "repaired" things that were never broken. Which one of the following choices describes the best and fastest way to change this example of unethical employee behavior?

A) Post a description of corporate ethical principles in each garage.
B) Create a better screening program for new hires.
C) Eliminate the bonus.
D) Create an employee hotline or helpline.