A living being has .............. System.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Concept of Systems**:
- A system in biological terms refers to a set of interacting or interdependent components forming an integrated whole. In the context of living beings, we need to identify what type of system they represent.

2. **Thermodynamics and Living Organisms**:
- In thermodynamics, systems are categorized into three types: open, closed, and isolated. Living organisms are best described as open systems.

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