Final answer:
Martha's criterion for the Date Joined column should be 'Between #6/1/2010# And #6/30/2010#' to select members who joined the fitness center in June 2010.
Step-by-step explanation:
Martha needs to use a date range criterion for the Date Joined column in her query to find members who joined the fitness center between June 1 and June 30, 2010. The correct criterion to use in a query would be Between #6/1/2010# And #6/30/2010#. This instructs the database to include only the records where the Date Joined falls within the specified range of dates. The pound signs (#) are used in some database systems, like Microsoft Access, to denote date literals. Martha should replace this notation with the appropriate date format if she's using a different database system.