Question

read the passage.
the evolving human skeleton
our early ancestors were hunter - gatherers who obtained food by hunting and by searching for edible wild plants. they needed strong bones, including large, strong jaws that enabled them to eat tough, uncooked foods. when our ancestors developed agriculture, however, their diet changed. they began growing plants, such as grains and beans, and raising animals for food; they also started cooking their foods, making them softer and easier to chew. consequently, the human skeleton underwent radical changes. over time, the human jaw became smaller and changed shape. other bones also evolved, becoming lighter, especially in the joints, as a result of both dietary changes and a less active lifestyle.
what is the main, or central, idea of the passage?
as early humans developed agriculture, their bones changed significantly.
early humans ate uncooked meats and vegetables, so they needed strong jaws for chewing.

Explanation:

To determine the main idea, we analyze the passage. It starts by describing early human ancestors as hunter - gatherers with strong bones and jaws. Then it explains how the development of agriculture, changes in diet (growing plants, cooking food), and a less active lifestyle led to significant changes in the human skeleton, especially the jaw. The first option only focuses on why early humans needed strong jaws, which is a detail. The second option, "As early humans developed agriculture, their bones changed significantly", captures the overarching theme of how the development of agriculture (along with related dietary and lifestyle changes) led to skeletal changes.

Answer:

As early humans developed agriculture, their bones changed significantly.