Read the following statement and choose the correct option.
A. The first heart sound (lub) is associated with the closure of both semilunar valves.
The duration between the adjacent second heart sound and first heart sound is 0.3 seconds
C. The cardiac output is the stroke volume multiplied by the number of heartbeats per minute.

Options

A. A, B and c are correct
B. A,C are correct but B is incorrect
C. A is correct but B, C are incorrect
D. A,B are incorrect but C is correct

Answer

To solve the question, we need to analyze each of the three statements provided and determine their correctness based on our knowledge of the cardiac cycle and heart sounds.

### Step-by-Step Solution:

1. **Evaluate Statement A:**
- **Statement:** "The first heart sound (lub) is associated with the closure of both semilunar valves."
- **Analysis:** The first heart sound (lub) is actually caused by the closure of the atrioventricular (AV) valves, specifically the bicuspid (mitral) and tricuspid valves, not the semilunar valves. Therefore, this statement is **incorrect**.

2. **Evaluate Statement B:**
- **Statement:** "The duration between the adjacent second heart sound and first heart sound is 0.3 seconds."
- **Analysis:** The cardiac cycle typically lasts about 0.8 seconds in a resting heart rate of about 72 beats per minute. The time between the first and second heart sounds is much shorter than 0.3 seconds. Thus, this statement is also **incorrect**.

3. **Evaluate Statement C:**
- **Statement:** "The cardiac output is the stroke volume multiplied by the number of heartbeats per minute."
- **Analysis:** This statement is correct. Cardiac output (CO) is indeed calculated as the stroke volume (SV) multiplied by the heart rate (HR). This means CO = SV × HR. Therefore, this statement is **correct**.

### Conclusion:
- **Correct Answer:** Only Statement C is correct. Therefore, the correct option is **C**.