Answer the following question given this paragraph: 

The cell is the smallest unit of structure and function of all living organisms. A cell is also the smallest unit of life, with single-celled organisms present on this planet for over 3.5 billion years. Single-celled ( unicellular ) organisms like bacteria are obviously composed of just one cell, whereas multicellular organisms can be composed of trillions of cells. Multicellular organisms include protists (though single-celled protists also exist), fungi, plants and animals. Most plant and animal cells are between 1 and 100 µm and therefore can only be observed under the microscope.


Q: What is the smallest unit of structure and function of all living organisms?

 Choices:

- chromosome

- organelle

- organ

- the cell

A:
the cell
