It is found that many insecticides - used to kill insects - lose their effectiveness after some years. What could be the cause of this? A) The insecticides are equally effective - such myths are spread by manufacturers so that they can sell more.

B) The species targeted by the insecticide are destroyed, but new insects which are unaffected, are born.

C) The insects develop resistance to the insecticide, which is passed on to successive generations.

D)The atmosphere contains so much of the insecticide that humans start being poisoned by it.