How does a multicellular organism develop? one cell grows bigger. the cells shrink. the cells differentiate. the cells replicate to form exact copies.

The cells differentiate.

Explanation:

In biology, differentiation refers to the gradual formation of organs or parts by a process of evolution or development, as when the seed develops the root and the stem, the initial stem develops the leaf, branches, and flower buds;

OR

in animal life, when the germ cell evolves the digestive and other organs and members, or when the animals as they advance in organization acquire special organs for specific purposes.

Note that option A and D explains organism growth NOT development

The cells replicate to form exact copies

Explanation:

Multicellular organisms develop by proliferating to produce many more cells. The process starts with a single fertilized cell that increasingly divides to form many more cells.