Which of the Following Would Be Classified as an External

Which of the following would be classified as an external cost (negative externality) ?

A) You are not able to study at night because there is so much noise coming from the room next to yours.
B) A private firm will not provide national defence since it is impossible to confine the benefits to only those individuals who have paid for it.
C) When you purchase a product, the cost is higher than you originally anticipated.
D) As more firms began hiring computer programmers, the salaries of computer programmers increased and therefore the firm's cost of production increased.