In closed circulatory system

Options

A. The cells and tissues are directly bathed in the blood pumped out by heart
B. Arteries and veins are lacking
C. The capillaries are largest blood vessels and closed at their ends
D. blood circulatews through a series of vessels of varying diameters.

Explanation

### Step-by-Step Solution:

1. **Understanding Closed Circulatory System**:
- In a closed circulatory system, blood is contained within vessels. This is different from an open circulatory system where blood bathes the organs directly.

2. **Analyzing the Options**:
- **Option 1**: "The cells and tissues are directly bathed in the blood pumped out by the heart."
- This describes an open circulatory system, not a closed one. Therefore, this option is incorrect.

- **Option 2**: "Arteries and veins are lacking."
- In a closed circulatory system, arteries and veins are present. This option is also incorrect.

- **Option 3**: "The capillaries are the largest blood vessels and closed at their ends."
- This is incorrect because the largest blood vessels are arteries, not capillaries. Capillaries are small and are not closed at their ends.

- **Option 4**: "Blood circulates through a series of vessels of varying diameters."
- This accurately describes a closed circulatory system, where blood flows through arteries, veins, and capillaries of different sizes. Thus, this option is correct.

3. **Conclusion**:
- The correct answer is **Option 4**: "Blood circulates through a series of vessels of varying diameters."