Which choice indicates an activity that lacks necessity for the event being discussed?

The choice that indicates an activity lacking necessity for the event being discussed is buying a new dress. This choice suggests a personal decision that may enhance one’s appearance or enjoyment for the occasion, but it is not an essential requirement for participating in the event.

In contrast, wearing colorful clothes might be tied to a theme or dress code, buying a special gift could be a socially expected gesture, and bringing a friend might be important for support or company, depending on the nature of the event. Therefore, while buying a new dress can be a nice addition, it does not serve as a prerequisite for attending or enjoying the event.