The number of the students who can attend this course ______ fifteen.

A．wonder what to do in the future
B．pay no attention to the UN’s call
C．take no measure in conservation
D．should act quickly to answer the UN’s call

A．a record calling on people to conserve nature
B．a rule worked out by the United Nations
C．an important book published in 1970
D．an idea that nobody would accept