【单选题】

{{I}}Questions 14 to 17 are based on the following passage.At the end of the passage, you will be given 20 seconds to answer the questions. Now listen to the passage.{{/I}} What is the main topic of this passage

A、The gathering of a film cluB、
B．The study of the elements of a petroleum-free community.
C．The division of labour among the members of a community.
D．The research program of alternate energy sources.