Mark the letter A B C or D to indicate the option that best completes each of the following exchanges, Mark the letter A; B; C; or D to indicate the option that best completes each of the following exchanges, Mark the letter A; B; C or D to indicate the option that best completes each of the following exchanges, Mark the letter A. B. C or D to indicate the option that best completes each of the following exchanges., Mark the letter A. B. C. or D to indicate the option that best completes each of the following exchanges.