Suppose Mary is willing to pay up to $15,000 for an used Ford pick-up truck. If she buys one for $12,000, her _ would be _.

Suppose Mary is willing to pay up to $15,000 for an used Ford pick-up truck. If she buys one for $12,000, her _ would be _.
A.benefit; $12,000
B.economic surplus; $12,000
C.cost; $15,000
D.economic surplus; $3,000
正确答案：economic surplus; $3,000