Unicellular microscopic organisms were first studied by

Options

A. Robert Hooke
B. Priestley
C. Pasteur
D. Leeuwenhoek.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the scientist who first studied unicellular microscopic organisms. These organisms are characterized by having a single cell and are often referred to as prokaryotes.

2. **Identifying Key Scientists**: The options provided include Robert Hooke, Presley, Pasteur, Oyer, and Leeuwenhoek. We need to determine which of these scientists is known for studying unicellular organisms.

3. **Robert Hooke's Contribution**: Robert Hooke is known for his discovery of cells in 1665 when he observed cork cells under a microscope. However, his work primarily focused on multicellular organisms and not specifically on unicellular organisms.

4. **Antonie van Leeuwenhoek's Contribution**: Antonie van Leeuwenhoek is recognized as the first scientist to observe and describe unicellular organisms. In 1673, he used a simple microscope to observe living microorganisms, which he referred to as "animalcules".

5. **Conclusion**: Based on the historical contributions of these scientists, the correct answer to the question is Antonie van Leeuwenhoek, as he was the first to study unicellular microscopic organisms.

**Final Answer**: Unicellular microscopic organisms were first studied by Antonie van Leeuwenhoek.

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