Find the synonym of the underlined word. 

Dogs were kept as domestic animals by early nomadic hunters. 

NOmadic implies of, pertaining to, or being a nomadic tribe or nomadic herders. 2: a nomadic hobo who moves around aimlessly, frequently, or without a set pattern of movement.
Hunter implies It's a someone or animal that hunts and devours its target, usually for sustenance.

Domestic can relate to a range of aspects such as private, local, internal, tame, and so on. Domestic denotes tame in this context. Dogs were kept as domestic animals, which means they were treated as tamable creatures. As a result, option D is correct and the others are not since they do not supply sufficient information.

Hence, the correct option is option  D.