Teachers may instruct the students to read the explanations in the reading skill section of every unit.Then the teacher may call upon them at random to explain the parts in their own words and assign them a grade for their explanation.The teacher should also ask for the definitions of technical terms: situational sets，semantic sets，associative field，and so on，and should return to these definitions from time to time in subsequent class meetings to ensure that the students remember them. This suggestion is made in order to encourage active learning （where the students are responsible for their learning），rather than passive learning （where the teacher is responsible for everything）.