13 Complete the text using the new words. Everyone knows that life in the modern world has become rather d (1). In big cities there are a lot of f (2) s and cars that p (3) the air. The water is p (4) too because factories and plants p (5) their w (6) into the rivers, lakes and seas. In the country the e (7) can be also p (8). People d (9) the industrial and domestic w (10) everywhere: in the forests, fields, near the rivers and lakes. The food people eat is not always h (11). All these are seri- ous e(12) problems and we must solve them soon.