The correct answer is A. Molecules
Explanation:
Molecules, which are atoms bonded together, are the basic unit for compounds and life. In the case of molecules that are essential for life, these are known as biomolecules and are the units for cells and therefore for tissues, organs, organ systems, and organisms. These molecules include proteins, nucleic acids, carbohydrates, etc. that play an essential role in basic functions for life. This implies the level that is lower than cells are molecules; also, organs, organ systems, and tissues are higher than cells as these are composed of groups of cells.
