Orcas, or killer whales, are the largest of the dolphins and one of the world's most powerful animals feeding on meat. They feast on marine mammals such as seals, sea lions, and even whales, employing teeth that can be four inches (ten centimeters) long. They are known to grab seals right off the ice. They also eat fish, squid , and seabirds. Though they often frequent cold, coastal waters, orcas can be found from the polar regions to the Equator . Killer whales hunt in deadly groups, family groups of up to 40 individuals. There appear to be both permanent and temporary group populations of killer whales. These different groups may hunt different animals and use different techniques to catch them. Permanent groups tend to prefer fish, while temporary groups target marine mammals. All groups use effective, cooperative hunting techniques that some are similar to the behavior of wolf packs. Whales make a wide variety of communicative sounds, and each group has various noises that its members will recognize even at a distance. They use echolocation to communicate and hunt, making sounds that travel underwater until they meet objects, then reflect back, showing their location, size, and shape. Killer whales are protective of their young, and other adolescent females often assist the mother in caring for them. Mothers give birth every three to ten years, after a 17-month pregnancy. Killer whales are immediately recognizable by their special black-and-white coloring and are the intelligent, trainable stars of many aquarium shows. Killer whales have never been widely hunted by humans. We can conclude that _ . A) people can find killer whales everywhere around the world B) killer whales live in different groups and never live alone C) by making sounds killer whales hunt and communicate D) humans' hunt has made killer whales being endangered
A:
C