Why Is Bentham Interested in Measuring the "Value" of a Pleasure

Why is Bentham interested in measuring the "value" of a pleasure or pain?

A) Because he wants to prove that actions that most people regard as morally good tend to promote the happiness of all affected.
B) Because he needs to show that only pleasures and pains have genuine value to show that the principle of utility is the sole principle of morality.
C) Because he wants to prove that some pleasures have a greater value than others.
D) Because we must be able to calculate how much pleasure and pain a particular action would cause to determine whether it conforms to the principle of utility.