Fill in each numbered blank in the passage with one most suitable word

VIII- Fill in each numbered blank in the passage with one most suitable word.
Rivers are ___1___ of the world's most important natural resources. Many
cities are on large rivers, and almost every country has ___2__ least one river that
__3__ an important part in the lives of its people.
Besides transportation, rivers ___4___ food, water for crops, water to drink,
and opportunities for recreation for people who live along their ___5___ . And in order
to get water for crops, engineers build a dam ___6___ a river and let the water become
5.

a lake ___7___ the dam. Then people can use their ____8___ not only to irrigate fields
but also to make electricity for homes and industries.
However, the water often becomes polluted when cities on river bank grow in
size and the number ___9___ industries increases. We are learning that it is necessary
to __10____ river clean if we want to enjoy the benefits of the natural resources.