Final answer:
The cell theory states that all organisms are made of cells, all cells come from pre-existing cells, and all life functions occur within cells.
Step-by-step explanation:
The cell theory is a foundational principle in biology. It posits that:
- All organisms are made of one or more cells.
- All cells come from pre-existing cells, showing that there is continuity of life.
- All life functions of organisms occur within cells, making them the basic unit of life.
Therefore, the correct answer to the student's question is:
d. All of the above
The cell theory fundamentally changed our understanding of life and emphasizes that cells are the building blocks of all living organisms, regardless of complexity.