Of the following, which is NOT true about international banking and payments? a. A commercial letter of credit offers payment protection to both parties. b. Payment in advance does not expose the importer to some risk concerning delivery of the goods. c. A commercial letter of credit is usually irrevocable. d. Payment in advance is the safest method. e. An open account is a simple agreement wherein be exporter sends an invoice with the goods and the exporter pays upon the receip