In the Cash Discount $500 4/10 Net 30, the Number

In the cash discount $500 4/10 net 30, the number 4 refers to

A) the percentage markup on the original unit.
B) the percentage discounted if the bill is paid within 10 days.
C) the percentage increase in price if the bill is not paid within 10days.
D) the discount in dollars per unit awarded if the order is paid on time.
E) the penalty in dollars if the bill is not paid within 10days.