Which class of macromolecules is primarily used as rapidly available energy sources by living thing?

The correct answer is - carbohydrates.

Explanation:

The four significant groups of macromolecules found in living beings are carbohydrates, lipids, nucleic acids, and proteins. carbohydrates comprised of carbon, hydrogen, and oxygen molecules, generally in a proportion of 1 : 2 : 1.

Living things use carbohydrates as their main form of energy.  Carbohydrates are a class of macromolecules is essentially utilized as a quickly accessible energy source by living things.

Thus, the correct answer is - carbohydrates.

which

what is a measurement of the earth’s history divided into time periods?

> fossil record <

sedimentary rock

> geologic time scale <

radioactive elements