Which of the Following Best Completes the Definition of Opportunity

Which of the following best completes the definition of opportunity cost? The opportunity cost of choosing any one alternative is the

A) market cost of the next best alternative.
B) value of the next best alternative that is given up.
C) the revenues that would be given up if that alternative is not chosen.
D) value of all other alternatives combined.
E) value of resources used to make that alternative available to the market.