In entering the billing address for a new client in Emil Company’s computerized database, a
clerk erroneously entered a nonexistent zip code. As a result, the first month’s bill mailed to
the new client was returned to Emil Company. Which one of the following would most likely
have led to discovery of the error at the time of entry into Emil Company’s computerized
database?

Answer (B) is correct.
In validity tests, values entered into the system are compared against
master files of valid data. In this case, a master file of all zip codes
recognized in the U.S. is held in memory and each time a clerk enters
data in the zip code field, the clerk’s entry is compared to the list of valid
values. If the zip code entered does not match any entry in the master
file, data entry is halted and the clerk is advised to reenter the data.