Cyanobacteria, unlike other types of bacteria that photosynthesize, do :
(a) not have a cell wall
(b) not have chlorophyll
(c) give off oxygen
(d) not give off oxygen

Options

A. not have a cell wall
B. not have chlorophyll
C. give off oxygen
D. not give off oxygen

Explanation

To solve the question regarding cyanobacteria, we need to analyze each option provided and determine which one is correct based on the characteristics of cyanobacteria.

### Step-by-Step Solution:

1. **Understanding Cyanobacteria**:
- Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria. They are among the earliest organisms on Earth and are capable of photosynthesis.

2. **Analyzing Option (a)**:
- "Not have a cell wall": This statement is incorrect. Cyanobacteria do have a cell wall, which is a characteristic feature of all bacteria.

3. **Analyzing Option (b)**:
- "Not have chlorophyll": This statement is also incorrect. Cyanobacteria contain chlorophyll a, which is essential for photosynthesis.

4. **Analyzing Option (c)**:
- "Give off oxygen": This statement is correct. Cyanobacteria perform photosynthesis and release oxygen as a byproduct, which is a significant contribution to the Earth's atmosphere.

5. **Analyzing Option (d)**:
- "Not give off oxygen": This statement is incorrect. As mentioned, cyanobacteria do release oxygen during photosynthesis.

6. **Conclusion**:
- The only correct option is (c) "give off oxygen."

### Final Answer:
(c) give off oxygen