Aerobic Respiration is the process in which complex molecules are changed into simpler molecules :

Options

A. In the presence of `O_(2)`
B. In the absence of `O_(2)`
C. Both (A) and (B)
D. None of the above.

Answer

### Step-by-Step Solution:

1. **Understanding Aerobic Respiration**:
- Aerobic respiration is a biological process that occurs in the presence of oxygen. It involves the breakdown of complex molecules into simpler ones to release energy.

2. **Identifying the Complex Molecules**:
- The primary substrate for aerobic respiration is glucose, which is a complex carbohydrate. Other substrates can include fats and proteins, but glucose is the most significant.

3. **The Process of Aerobic Respiration**:
- Aerobic respiration takes place in the mitochondria of cells. The overall reaction can be summarized as:
\[ \text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water} + \text{Energy (ATP)} \]
- Here, glucose is converted into carbon dioxide and water, releasing energy in the form of ATP (adenosine triphosphate).

4. **Conclusion**:
- In aerobic respiration, complex molecules (like glucose) are broken down into simpler molecules (like carbon dioxide and water) in the presence of oxygen, resulting in the production of energy (ATP).

5. **Correct Answer**:
- Based on the understanding that aerobic respiration occurs in the presence of oxygen and involves the conversion of complex molecules to simpler ones, the correct answer to the question is that aerobic respiration is indeed the process in which complex molecules are changed into simpler molecules in the presence of oxygen.