According to cell theory, what do these four organisms have in common? A) They are made of one or more cells. B) They must undergo sexual reproduction. C) They have a nucleus or control center. D) They require carbon dioxide to produce food.

A) They are made of one or more cells

Explanation:

Cell theory states that:

1. All organisms are composed of one or more cells, and the life processes of metabolism and hereditary occur within these cells

2. Cells are the smallest living things, the basic unit of organisation of all organisms

3. New cells arise only by division of pre-existing cells

d) a person who learns about the world by observing it.

explanation:

scientist are people who discover why and how things are done and made in the world.