Nomadic families living in the Arabia were organized into tribes-their government

Those nomadic families were called the Bedouin.

Explanation:

They're a collection of small nomadic families that usually travels between Africa and Arabian Peninsula. Most of them make a living by herding Camels or other forms of animals that commonly found in that area.

Different Bedouin families usually gathered together to form a clan and developed their own independent way to govern. Keeping this form of government make it easier for them to organize when they need to move to other place when they're seeking resources.

a was not the right answer