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.

first, the romans stayed isolated because they had to defend their own territories from neighboring cities that were harassing them, like the etruscans. second, once the romans managed to defeat their neighbors, and started to expand their territory, they started to build roads and bridges. finally, now that the romans have covered their territory with roads functioning as highways, they could mobilize their legions faster to assemble larger military units in a specific place.

answer; the federal reserve system;