Use the given words in the appropriate forms to complete the sentences

1. Practically no one can grow up in the world today without
   [ ] into contact with chalk at some time of
   [ ] life.
2. Every year thousands of people suffer from the flu and, unfortunately, this
   [ ] likely to continue. Although scientists
   [ ] to understand the flu, there are some ways to avoid
   [ ] it. You may try them
   [ ].
3. Diamonds are the
   [ ] natural substance
   [ ] to man.
4. X-rays
   [ ] in Germany in 1895 by Wilhelm Roentgen, and thus now sometimes
   [ ] "Roentgen rays".
5. Oxygen is one of the
   [ ] elements in nature.
6. The Gulf Stream
   [ ] an ocean current, the
   [ ] current of all. It is like a river that
   [ ] through the sea instead of on land. The Gulf Stream is so vast that it is
   [ ] than all the rivers in the world put together.
7. People who raid the fridge in the middle of the night may be suffering from a genuine medical complaint and not just hunger pangs. Scientists
   [ ] biochemical differences in the
   [ ] of people who experience uncontrollable urges to eat late at night.
8. In many ways, the oceans still remain a great mystery to
   [ ]. Man
   [ ] how old oceans are. It
   [ ] certain that in the
   [ ] stages of the earth's growth no oceans
   [ ].