Suppose that the extra cost to Tim of a third glass of soda is zero because he's at a restaurant that gives free refills. According to the Cost-Benefit Principle Tim should:

A、not drink a third glass of soda.;

B、drink a third glass of soda if his total benefit from drinking soda is positive.;

C、drink a third glass of soda.;

D、drink a third glass of soda if the extra benefit of doing so is positive.