The correct answer is cell theory.
It states that :
1. All living organisms are made of cells.
2. The cell is the basic unit of life
3. Cells arise from pre - existing cells.
The modern version of cell theory adds the following:
4. Energy flow occurs within cells.
5. Hereditary information, namely DNA, is passed from cell to cell.
6. All cells have the same basic chemical composition.
The cell theory was proposed by three German scientists called Theodore Schwan, Rudolf Virchow and Mathias Schleiden.