Questions 14-17 are based on the following dialogue between classmates about their presentation. You now have 20 seconds to read Questions 14-17. What are the students doing when the man arrives in the class

A．How to make the coronary bypass operation.
B．An objective introduction of the coronary bypass operation.
C．The controversy within the medical profession on the coronary bypass procedure.
D．A complete refusal of coronary bypass operation

A．indicate the theme of the passage
B．explain why every group has a culture of its own
C．introduce the similarity of non-superiority in culture and language
D．start up the speech

A．to
B．on
C．in
D．for