Read the following passage, then choose the correct answer to questions.

      Water is one of our most precious resources; put it simply, without water there would be no life.Unfortunately, many of us seem to have (21)_______ this fact, and as a result the world is facing the danger of running (22)_______ water.The actual (23)_______ of water on earth has changed little since the time of dinosaurs.The problem has been caused by people’s misuse of our water supply.This not only means that we have polluted our rivers and seas, but also that we are (24)_______ a great deal of this precious resource.Unfortunately the destruction of the rain forests has (25)_______ this problem worse since much of the rain that falls is lost because it runs off into the sea.The population of the earth is increasing daily, so it is vital that we (26)_______ a solution to this problem before it is too late.