关于discount的问题

1.Avalon gives his customers individual trade discounts from the list price and a general 5% cash discount for all invoices settled within 7 days of issue.A new customer,Nolava negotiates a 25% trade discount.His transactions during June are:
June 12 Buys goods with a $5000 list price
June 15 Returns goods with a $1000 list price as faulty
June 16 Pays half of the net balance on his account

How much does Nolava owe Avalon at the end of June?
A.$1,425
B.$1,500
C.$2,000
D.$2,850
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选B.我想问的是这个cash discount这里是怎么回事？？

现金返还