Which term correctly identifies the way in which students were invited to participate in the debate club?

The correct term that identifies how students were invited to participate in the debate club is "Flyer." Flyers are typically designed to be distributed in large quantities to publicize an event, such as a club meeting or a special activity, and they often contain a call to action, encouraging students to join or participate. They are usually colorful, eye-catching, and provide specific details about the event, including the date, time, and location.

While the other options may also involve communicating information about events or activities, a bulletin typically refers to an official announcement or report, often more formal and less visually appealing than a flyer. Posters are often larger and used for more permanent displays rather than for distribution, and newsletters are regularly distributed publications that include updates and news over a period, rather than a singular invitation to an event. Thus, a flyer is the most fitting choice for inviting students to participate in the debate club.