The teacher opens the CD twice so that the students listen and answer the questions in section 1, the students all answering questions of their own before the teacher will reveal the answers.
Teachers open the two CDs to listen to the students and answered questions in one. Then the whole class to answer their questions before the teacher will correct answers.
The teacher open the CD 2 times to make the students listen and answer the questions in the 1. Then let students answer themselves before I will reveal the answer.