Which of the following is an example of open system?

Options

A. Human body
B. The earth
C. Pond
D. All of these

Answer

To determine which of the following is an example of an open system, we need to understand the definition of an open system in thermodynamics.

### Step-by-Step Solution:

1. **Define Open System**: An open system is one that can exchange both energy and matter with its surroundings. This means that both heat (energy) and substances (matter) can flow in and out of the system.

2. **Identify Examples**: We need to analyze the options provided to see which one fits the definition of an open system. Common examples of open systems include:
- The human body: It exchanges energy and matter with the environment through processes like breathing and eating.
- A pond: It also exchanges energy (like heat from the sun) and matter (like water, nutrients, and organisms) with its surroundings.

3. **Evaluate Other Options**:
- The Earth: While it does exchange energy (like sunlight) with space, it is often considered a closed system in terms of matter because the amount of matter (like the total mass of the Earth) remains relatively constant over time.

4. **Conclusion**: Based on the analysis, the human body and a pond are both examples of open systems. Therefore, if asked for an example of an open system, the correct answers would be the human body and a pond.

### Final Answer:
The human body is an example of an open system.