Questions: True brachiation is found in: Old World monkeys chimpanzees and gorillas New World monkeys gibbons and siamangs

The answer is the fourth one (D): gibbons and siamangs.

Explanation for each option:

1. Old World monkeys: Incorrect. Old World monkeys, such as baboons and macaques, do not exhibit true brachiation. They are more terrestrial and do not have the anatomical adaptations for brachiation.

2. Chimpanzees and gorillas: Incorrect. While chimpanzees and gorillas can swing from branches, they do not exhibit true brachiation. They are more adapted to knuckle-walking and climbing.

3. New World monkeys: Incorrect. Some New World monkeys, like spider monkeys, can swing through trees, but they do not exhibit true brachiation. They often use their prehensile tails for support.

4. Gibbons and siamangs: Correct. Gibbons and siamangs are known for true brachiation. They have long arms and a shoulder structure that allows them to swing efficiently from branch to branch, making them the most proficient brachiators among primates.

In summary, true brachiation is found in gibbons and siamangs.