Final answer:
The primary adaptation of hominids is bipedalism, allowing them to free up their hands, increase energy efficiency, and thermoregulate.
Step-by-step explanation:
The primary adaptation of hominids is bipedalism, which means walking on two feet.
This adaptation allowed hominids to free up their hands, enabling them to carry tools, food, or offspring. Bipedalism also increased energy efficiency and thermoregulation by exposing more of the body's surface.