Which one is NOT mentioned in this passage that can be the source of carbon dioxide

A．they think that carbon is beneficial for plant growth
B．they want to use more fuels that can emit carbon dioxide
C．they think carbon dioxide is not the main reason for global warming
D．they think it will destroy the natural balance of gases in the world

A．to give advice on appropriate conduct for social occasions
B．to provide ways of how to obtain information about people
C．to call the reader's attention to the negative side of people's characters
D．to discuss the various aspects of getting to know people