Cell theory was formulated by

Options

A. Schleiden and Schwann
B. Robert Hooke
C. Leeuwenhoek
D. Marcello Malpighi.

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks who formulated the cell theory.

2. **Recall Key Scientists**: The cell theory was formulated by two key scientists: Theodor Schwann and Matthias Schleiden.

3. **Understand the Cell Theory**:
- The cell theory states that all living organisms are made up of cells.
- Cells are the basic structural and functional units of life.
- New cells arise from pre-existing cells through cell division.

4. **Summarize the Contributions**:
- Theodor Schwann contributed to the understanding that animals are made of cells.
- Matthias Schleiden contributed to the understanding that plants are also made of cells.

5. **Conclude the Answer**: Therefore, the cell theory was formulated by Theodor Schwann and Matthias Schleiden.

**Final Answer**: The cell theory was formulated by Theodor Schwann and Matthias Schleiden.

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