Explanation:

Magnetism is a property of certain materials that causes them to attract or repel other materials. The surest test for magnetism involves observing the behavior of the material in the presence of another magnet.

Attraction and Repulsion:
- When two magnets are brought close to each other, they can either attract or repel each other, depending on their orientations.
- Like poles (north and north or south and south) repel each other, causing a force that pushes the magnets away from each other.
- Unlike poles (north and south) attract each other, causing a force that pulls the magnets towards each other.

Attraction Only:
- If a material is attracted to a magnet, it indicates that the material is magnetic.
- However, this does not necessarily mean that the material is a permanent magnet. It could be a temporary magnet or a material that becomes magnetized in the presence of a magnetic field.

Repulsion Only:
- If a material repels a magnet, it indicates that the material is not magnetic.
- Non-magnetic materials, such as wood or plastic, do not have magnetic properties and therefore do not exhibit attraction towards magnets.

Conclusion:
The surest test for magnetism is observing whether the material repels a magnet. If the material repels the magnet, it indicates that the material is not magnetic. If the material attracts the magnet, it indicates that the material is magnetic, but further tests would be required to determine if it is a permanent magnet or a temporary magnet. Therefore, the correct answer is option 'C', which states that the surest test for magnetism is repulsion only.

Correct answer is option C