Why Do People Typically Engage in Whistle-Blowing

Why do people typically engage in whistle-blowing?

A) They lack the power to change the practice they see as undesirable.
B) It is easier to bring the practice to someone else's attention rather than handle it themselves.
C) Employees are usually given a promotion for highlighting poor business practices.
D) They don't like the offending employee and want to see him or her get in trouble.