Ais a small number of people with complementary skills who are committed to a common purpose, performance goals, and approach for which they hold themselves mutually accountable.
a. formal group
b. teamvirtual team
c. mature group
d. informal group

Inormal Group

Explanation:

It's an informal group because Formal Groups are bigger, and aren't mutually accountable since they have a leader, while informal groups doesn't have any.

answer; genetics;

the answer to your question is,

old stone age.

-mabel < 3