5.( ) Memory is ________ that we
keep in our mind and carry about.
A.
the best diary B.
the best camera
C. a
great help D.
a beautiful picture
(B)
The world
is not only hungry, it will also be thirsty for water. About 97% of water on
the earth is sea water, or salt water. Man can only drink or use the other 3%of the fresh water (淡水)which comes from
rivers, lakes and underground. On the other hand, because the number of people
in the world is becoming larger and larger, more and more fresh water is needed.
So water shortage becomes a big problem.
How can
we work out this problem? Scientists have found some ways to turn salt water
into fresh water. One important way is to boil (使达到沸点)sea water with high heat until vapor (蒸汽)rises, leaving the
salt. In this way, a lot of fresh water can be made quickly.
But
heating is not the only way to get fresh water. Other ways are tried, for
example, digging deep wells, keeping rain water and preventing rivers from
being polluted.
Which way
is the best? To get the most fresh water for the least money is the best.