One of the following example of action of autonomic nervous system is :

Options

A. Knee-jerk reflex
B. Pupillary reflex
C. Swallowing of food
D. Peristalsis of intestine

Answer

To determine an example of the action of the autonomic nervous system from the given options, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Autonomic Nervous System (ANS)**:
- The autonomic nervous system is responsible for regulating involuntary body functions such as heart rate, respiratory rate, digestion, and urination. It operates without conscious control.

2. **Analyzing the Options**:
- **Option 1: Knee Jerk Reflex**:
- This reflex is a simple monosynaptic reflex that involves a direct connection between a sensory neuron and a motor neuron in the spinal cord. It is a voluntary response and not controlled by the autonomic nervous system. Therefore, this option is incorrect.

- **Option 2: Pupillary Reflex**:
- The pupillary reflex controls the diameter of the pupil in response to light intensity. While it involves involuntary control, it is primarily mediated by the somatic nervous system rather than the autonomic nervous system. Thus, this option is also incorrect.

- **Option 3: Swallowing of Food**:
- Swallowing is an involuntary reflex that involves several muscles and is controlled by the central nervous system. However, it is not primarily an action of the autonomic nervous system, as it involves voluntary control as well. Therefore, this option is incorrect.

- **Option 4: Peristalsis of Intestine**:
- Peristalsis refers to the involuntary contractions of the muscles in the digestive tract that move food along the intestines. This action is regulated by the autonomic nervous system, specifically the enteric nervous system, which controls digestive processes. Hence, this option is correct.

3. **Conclusion**:
- The correct answer is **Peristalsis of Intestine**, as it is an action regulated by the autonomic nervous system.

### Final Answer:
The example of an action of the autonomic nervous system is **Peristalsis of Intestine**.