This is an organism that relies on complex organic substances for nutrition.

The correct answer is - heterotroph.

Explanation:

A heterotroph is a group of organisms that depends on then the other organic carbon substances which are complex for their nutrition, mostly on animals and plants matter.

Heterotrophs in a food chain can be a primary, secondary or tertiary consumers but can not be producers as they do not produce their food.  The examples of the heterotrops are human, animals, and other primary, secondary or tertiary consumers.

Thus, the correct answer is -Heterotrophs.

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.