If water pollution continues at its present rate, it will eventually

Answer: (c) make oxygen molecules unavailable to water plants

Organic pollution feeds microbes that use up dissolved oxygen, leaving too little for water life.

The idea

The most common water pollutant is organic waste: sewage, food waste, farm run-off. Its main damage is indirect. Microbes that break it down use up the oxygen dissolved in the water, and then everything else that needs oxygen suffers.

Organic waste and nutrients enter water → Algae and microbes multiply → Their respiration and decay use up oxygen → Water plants and animals are left without oxygen → The water body dies

Why the others are wrong

(a) The water cycle runs on solar energy; pollution can’t stop it.

(b) Pollution doesn’t stop rain.

(d) Pollution usually adds nitrates (eutrophication), not removes them.

The trap

(d) reverses what pollution does to nitrates.

Also know

Water plants need oxygen too: they respire all the time, and at night they take oxygen from the water. The water cycle is driven by the sun’s heat and cannot be stopped by pollution.