Communicative Language Teaching (CLT) originated from the changes in the British Situational Language Teaching approach dating from the late 1960s. Stemming from the socio-cognitive perspective of the socio-linguistic theory, with an emphasis on meaning and communication, and a goal to develop learners' "communicative competence", Communicative Language Teaching (CLT) approach evolves as a prominent language teaching method and gradually replaced the previous grammar-translation method and audio-lingual method. From the literal meaning, we can know that the main emphasis of "Communicative Approach" is "communication." So the main task of teachers is to teach students how to communicate in English efficiently. Under this precondition, "communication" is divided into several kinds of "functions," such as asking directions, ordering dishes at restaurants, buying airline tickets or chatting on the Internet. Each one is regarded as a function. When introducing one function, teachers give students some key words, sentences or phrases and design some activities for students to practice what they learn. The purpose is to train students to ask directions, order dishes at restaurants in English by themselves.
             As "communicative competence" is the desired goal, in CLT, meaning is important. In socio-cognitive perspectives, language is viewed as a vehicle of conveying meaning, and knowledge is transmitted through communication involving two parts, for example, speakers and listeners, and writers and readers, but is constructed through negotiation. As a consequence, "communication is not only a matter of following conventions but also of negotiating through and about the conventions themselves. It is a convention-creating as well as convention-following activity. Therefore, there are three elements involved in the underlying learning theory: communication principle, task-based principle, and meaningfulness principl...