Cosmos Corporation, which uses a perpetual inventory system, purchased $2,000 of merchandise on July 5 on account. Credit terms were 2/10, 1/30. It returned $400 of the merchandise on July 9. Which of the following is one effect when Cosmos pays its bill on July 21? O Debit to Accounts Payable for $2,000 O Debit to Cash for $1,600 O Credit to Cash for $1,600 O Credit to Accounts Payable for $1,600