Which of the following is a common type of memorial service?

A traditional memorial service and a celebration of life service are indeed common types of memorial services. A traditional memorial service typically takes place in a funeral home, church, or other venue and often incorporates solemn rituals and eulogies, focused on honoring the deceased's life and providing closure to attendees. This type of service follows conventional practices, including readings, music, and possibly an open casket experience.

On the other hand, a celebration of life service is more informal and emphasizes celebrating the individual’s life rather than focusing solely on grief. These services often include personal stories, music that the deceased enjoyed, and an atmosphere of remembrance that can be uplifting and positive.

While the other options present variations of memorial gatherings, they do not align as closely with commonly recognized categories of memorial services. Legal and online services, for instance, are not conventional types of memorial services, and a public gathering, though it can sometimes overlap, is broader and lacks the distinct focus on memorialization that characterizes the other two services. Similarly, a private remembrance may be more personal and familial but doesn't fit into the standard definitions and practices of memorial services like those mentioned in the correct answer.