我们需要一种不会污染环境的燃料。

We need a fuel that won't ___pollute the environment.

它们大多数不污染环境，而且不会造成道路拥堵。

Most of them don't ___pollute the environment, and they don't create traffic jams on the roads.

工厂经常用化学废物污染河流。

Factories often ___pollute the river with chemical waste.