By determining the density of the object
The three major types of pollution are air pollution, water pollution, and land pollution. Sometimes, air pollution is visible. A person can see dark smoke pour from the exhaust pipes of large trucks or factories, for example. More often, however, air pollution is invisible.
The eggs of the fluke are passed into water supplies from feces and urine of infected people. After hatching the parasite actively swims and invades the body of a snail, usually by penetrating through the snail's foot. The parasite requires the presence of certain species of snails (e.g., Oncomelania, Biomphalaria, Bulinus) to transform (and multiply) itself into an infective stage, called cercaria.
Only DNA contains the base, thymine, which binds with adenine. Whereas RNA contains the base, uracil, which binds with adenine. Also the structure of their sugars are different: Deoxyribose, in DNA, contains one less oxygen than RNA's ribose sugar.