All unicellular organisms with a true nucleus were included in the kingdom:
(a) Monera
(b) Protista
(c) Fungi
(d) Protozoa

Options

A. Monera
B. Protista
C. Fungi
D. Protozoa

Explanation

To solve the question "All unicellular organisms with a true nucleus were included in the kingdom:", we need to analyze the options provided:

1. **Understanding the Options**:
- (a) **Monera**: This kingdom includes prokaryotic organisms, which do not have a true nucleus. Therefore, this option cannot be correct.
- (b) **Protista**: This kingdom includes unicellular eukaryotic organisms, which possess a true nucleus. This option is a strong candidate for the correct answer.
- (c) **Fungi**: While fungi can be eukaryotic, they are primarily multicellular organisms. Some fungi are unicellular (like yeast), but not all. This option is not the best fit for the question.
- (d) **Protozoa**: This term refers to a phylum of unicellular eukaryotic organisms, not a kingdom. Therefore, this option is also not correct.

2. **Conclusion**:
- The only kingdom that includes all unicellular organisms with a true nucleus is **Protista**.

Thus, the correct answer is **(b) Protista**.