The Cash Discount Terms for a $500 Purchase Are 4/10

the cash discount terms for a $500 purchase are 4/10 net 30,the number 10 refers to

A) the percentage discounted if the bill is paid within 30 days.
B) the percentage increase in price if the bill is not paid within 10 days.
C) the number of days for which the discount is valid.
D) the discount in dollars per unit if the order is paid on time in 30 days.
E) the penalty in dollars if the bill is not paid within 10 days.