Here's why:

* Proteins are large, complex molecules that are essential for life. They perform a wide variety of functions in the body, such as building and repairing tissues, transporting nutrients, and fighting infections.

* Cells are the basic units of life. They contain many different structures and components, including proteins.

So, the correct answer is both.

You would find proteins *inside* cells. Proteins are the building blocks and workers of cells, so they are essential for their function.