Water pollution occurs when are released into the water supply.
a.
fish
b.
toxins
c.
small stones
d.
ultraviolet rays

Its B i just took the test

The answer is B.) Toxins.
Toxins pollute the water, can kill fish, and prevent anyone from going into the water to have fun.
You can also use the elimination process to figure out the answer.
Fish belong in water, UV rays have little to no effect when you're underwater, and small stones do not harm the environment of any water.

Europeans are more concentrated in urban areas.

What exactly do you mean