Please choose the correct answer to the question: Chimpanzees dig for insects with sticks; what is another example of using tools?

Answer1: birds using twigs to build nests Answer2: otters using rocks to open clams Answer3: anteaters using their tongue to catch ants Answer4: koalas using their pouch to hold infants

Answer format: answer1/answer2/answer3/answer4
Answer: answer2