A—-source of energy is a natural source that goes on providing energy without getting exhausted. (

Explanation

To solve the question, we need to fill in the blank with the correct term that describes a type of energy source. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Question
The question asks for a type of energy source that is natural and can provide energy continuously without being depleted.

### Step 2: Identify Key Characteristics
- The source must be natural.
- It should provide energy continuously.
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