Questions: Which of the following is an advantage of bipedalism in hominins? The hands are free to carry food, tools, and weapons.

The answer is the second one: The hands are free to carry food, tools, and weapons.

Explanation for each option:

1. "Standing on four feet elevates the head, making it easier to see over obstacles and to see farther to allow earlier detection of predators." - This statement is incorrect in the context of bipedalism. Bipedalism involves standing on two feet, not four. The advantage of bipedalism is that it elevates the head when standing on two feet, not four.

2. "The hands are free to carry food, tools, and weapons." - This is a correct advantage of bipedalism. By walking on two feet, hominins have their hands free, which allows them to carry objects, use tools, and perform other tasks that require manual dexterity.

3. "Walking on two feet requires more muscle groups and more energy than walking on all fours." - This statement is incorrect as an advantage. While it is true that bipedalism can be more energy-intensive in some contexts, it is not considered an advantage. The question asks for an advantage, and increased energy expenditure is generally a disadvantage.

4. "Standing on two feet makes it easier to climb trees." - This statement is incorrect. Bipedalism is not advantageous for climbing trees; in fact, it is generally less efficient for climbing compared to quadrupedalism or other forms of locomotion that involve using all four limbs.

In summary, the primary advantage of bipedalism in hominins is that it frees the hands for carrying and manipulating objects, which is crucial for tool use and other activities.