After supper he_______leisurely on the campus.

A．what is the greenhouse effect
B．how serious the greenhouse effect would be
C．it is important to reduce the use of fossil fuels
D．how to change the greenhouse effect

A．the author is worried about the greenhouse effect
B．the author asks all of us to reduce the use of coal
C．the greenhouse effect is welcome as it is a mixed blessing
D．the greenhouse effect has affected our life now