A．Scientists have managed to persuade industries to take measures to reduce emissions of gases into the atmosphere.
B．There is no general agreement on the causes and effects of acid rain yet.
C．Special glasshouses are set up in order to investigate the effects of air pollution on plants.
D．Ozone is mainly emitted by the oil refining industry,

A．It never notices any mistakes a child makes.
B．It never corrects any mistakes a child makes.
C．It often makes children correct their own mistakes.
D．It corrects children’s mistakes all the time.