Answer:
a. routine
a. Send a mass e-mail to all participants
Step-by-step explanation:
In this case, your message is routine, and it is best conveyed with a less-rich medium. People are familiar with the potluck, because it is a regularly scheduled event. If you send a mass e-mail, people will glance at it and assume that everything is fine. If you use a richer medium, such as a telephone message, people may wonder whether there is a hidden meaning behind your words. For example, they might wonder whether management will announce bad news at the potluck and wants to make sure everyone is there to hear it.