Sound requires a ................. for propagation.

Explanation

**Step-by-Step Solution:**

1. **Understanding Sound**: Sound is defined as a form of energy that is produced by vibrations. It travels through different mediums.

2. **Requirement for Propagation**: For sound to propagate, or travel, it needs something to carry those vibrations. This is essential because sound cannot travel through a vacuum where there is no matter.

3. **Identifying the Medium**: The substance through which sound travels is called a medium. This medium can be in the form of solids, liquids, or gases. Each of these states of matter can transmit sound waves due to their ability to vibrate.

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