4. Problem solving tasks: this task require students to solve the problems in real life according to their own knowledge and reasoning ability.

5. Memory challenge tasks: it demands students to finish reading an article in the prescriptive time, and then they summarize and retell the main content of the article or it requires students to ask several questions to improve their reading ability and memory ability.

6. Creative tasks: it refers to tasks with exploratory, openness and practicality. It includes a list, the arrangement of order and classification, the contrast and the settlement of tasks. In these tasks, team cooperation and organization skills play a very important role.

2.3 Previous Researches of TBLT文献综述

In the recent 20 years，the application for use as a linguistic task of classroom teaching is an important part of the study. The most famous one may be Bangalore Communicational Teaching Project by N·S·Prabhu ，hereinafter referred to as BCTE. But N·S·Prabhu wasn’t the first one who started it．Tasks in language teaching courses have been used for many years. But in Prabhu’s experiment，he first made the task as an important part of teaching．Prabhu defined the tasks in his Second Language Teaching like this: students are required by teachers and thinking process control and regulate the process and results of the activity. Task—Based Language Teaching is a language teaching method which started in the 1980s in Bangalore of India, where N·S·Prabhu also made a strong communicative experiment-Bangalore Project. This experiment may be regarded as the first attempt which takes the duty in class and has aroused the language teaching interest．From then on，Many linguists invest in the research upsurges．They all consider the tasks as the research center．With the deep research, task-based language teaching in the1990s gradually matures in theory. Prabhu’s book has carried on the limits in his Second Language Pedagogy(Prabhu, 1987:23)．He thought a task is an activity which is given by students when they are thinking of the information, and can make students control their own thinking process．He pides activities into these four kinds：rules of the center, form center, target center activities and significance of the center．He totally agreed on the last one．He thinks there is no need to teach the students too many grammar rules and correct those too often so as to make the students themselves learn internalization grammatical system when they focus on the meaning of language grammar system. This coincides with the concept of Natural way of Krashen. But Prabhu’s task—based language teaching is not complete，for instance，the choices of the tasks has no demand analysis，Also the tasks rating is arbitrary. And any forms of activity center in language teaching are rejection．(Long&Cmokers,1992:42)．These became the primary problems for the researchers．