The demand curve shows ( )
选项：

A:the highest price buyers actually pay for each unit of a good and the amount they would buy.;
B:the highest price buyers would be willing and able to pay for each unit of the good or the amount purchased at each price.;
C:the consumer surplus buyers gain from each unit of the good if they were to purchase it.;
D:the enjoyment consumers get from each unit of the good if they were to purchase.