다음 글의 밑줄 친 부분 중, 어법상 틀린 것은? [3점]
language is one of the primary features that distinguishes humans from other animals. many animals, including dolphins, whales, and birds, ①do indeed communicate with one another through patterned systems of sounds, scents, and other chemicals, or movements. furthermore, some nonhuman primates ②have been taught to use sign language to communicate with humans. however, the complexity of human language, its ability to convey nuanced emotions and ideas, and its importance for our existence as social animals ③setting it apart from the communication systems used by other animals. in many ways, language is the essence of culture. it provides the single most common variable ④by which different cultural groups are identified. language not only facilitates the cultural diffusion of innovations, it also helps to shape the way we think about, perceive, and ⑤name our environment.

답이 3번인데 .. 그 밖의 어법까지 자세한 설명 해주시겠어요