Emma and her friends traveled around China by（1）

and sometimes by（2）

.Five years ago，when Ben was in Beijing with his parents，they were caught in a sandstorm and it was difficult to breathe and the sand even（3）

people.But this time，Emma found that there were（4）

sandstorms in Beijing than before because people in Beijing are（5）

more trees.When Emma was in China，it was very hot.When she drank up the bottled water she took with her，she would drink from a river.Ben told Emma that it was dangerous because some rivers and lakes were polluted by（6）

.It would be（7）

for them to drink bottled water.