Final answer:
Atoms form the basic unit of a chemical element and when combined, they make up molecules. Cells are complex structures built from molecules, establishing that atoms precede molecules, which in turn precede cells.
Step-by-step explanation:
The correct statement is a. atom comes before the molecule. An atom is the smallest unit of a chemical element that retains its chemical properties. When atoms combine, they form molecules, which are compounds consisting of two or more atoms joined together. For example, a water molecule is composed of two hydrogen atoms and one oxygen atom (H2O).
Thus, in the context of biology, a cell is a more complex structure constructed from molecules, which in turn are made from atoms. The hierarchy described here starts at the atomic level, progresses to molecules, and then leads to cells and larger biological structures.