The correct answer is (a) Gibbon.
Gibbons are the smallest of the great apes, and they are also the most agile. They are found in the forests of Southeast Asia, and they spend most of their time in the trees. Gibbons are excellent climbers, and they use their long arms and tails to swing from branch to branch. They are also very vocal animals, and they communicate with each other using a variety of calls.
Chimpanzees are the next smallest of the great apes, and they are found in Africa. Chimpanzees are very intelligent animals, and they are known for their ability to use tools. They are also very social animals, and they live in groups of up to 100 individuals.
Gorillas are the largest of the great apes, and they are found in Africa. Gorillas are very powerful animals, and they are known for their strength and their size. They are also very gentle animals, and they live in groups of up to 30 individuals.
Orangutans are the third largest of the great apes, and they are found in Indonesia. Orangutans are very intelligent animals, and they are known for their ability to use tools. They are also very social animals, and they live in groups of up to 10 individuals.