Probably the largest group size that enables each member to interact easily with every other member is:

A) 8
B) 6
C) 12
D) 9

According to research, the largest group size that enables each member to interact easily with every other member is around 12. This is called the "dunbar number" and is based on the idea that humans are able to maintain stable relationships with up to around 150 people, but can only have close relationships with a smaller subset of that number. A group of 12 allows for enough diversity and interaction while still maintaining a sense of cohesiveness and connectedness.