It is widely accepted reported in the western media that the drug ______ is now becoming a leading cause of teenager crimes.

If we keep wasting so much energy, ________ are that our oil wells will dry up and the environment will be destroyed.

 Did you get much _____ from your holiday?

Pigeon is often considered a（n）________ of peace.

Hardly a month goes by without ______ of another survey revealing new depths of scientific illiteracy among US citizens.