Resale price maintenance occurs when:
A) a retailer refuses to lower its price, even though competitors have lowered their prices.
B) a wholesaler refuses to offer volume discounts to its high-volume customers.
C) a manufacturer sells its products only to those dealers who agree to charge a certain price for the product's resale.
D) a manufacturer sells its products to its dealers for the same price in all states, even though the retail market is much more competitive in some states than in other states.
E) competitors agree to sell their products for the same price.