The correct answer is A. Octopus.
An octopus is a cephalopod mollusk of the order Octopoda. Octopuses have two eyes and four pairs of arms and, like other cephalopods, they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms.
Octopuses have a complex nervous system and are capable of learning and problem-solving. They are also able to change their skin color and texture to camouflage themselves or to communicate with other octopuses.
The largest octopus species is the giant Pacific octopus, which can grow to a mantle length of 13 feet (4 meters) and weigh up to 600 pounds (272 kilograms).
B. Squid are also cephalopods, but they have ten arms instead of eight. Squid are also much smaller than octopuses, with the largest species, the colossal squid, reaching a mantle length of 14 feet (4.3 meters) and weighing up to 495 pounds (224 kilograms).
C. Coral are marine invertebrates that live in colonies. Coral are not animals, but rather colonies of tiny animals called polyps. Coral polyps are related to jellyfish and anemones.
D. Jellyfish are also marine invertebrates, but they are not related to octopuses, squid, or coral. Jellyfish are cnidarians, which means that they have stinging tentacles. Jellyfish are very diverse, with over 20,000 species.