4) The firm does atomic research for Dr. Xavier of the X-Men, invoicing that customer $2,000. a) debit Revenue 2,000, credit Accounts Payable 2,000 b) debit Cash 2,000, credit Revenue 2,000 c) debit Accounts Receivable 2,000, credit Revenue 2,000 d) debit Accounts Payable 2,000, credit Revenue 2,000