Biology

The correct answer is: A.Abundance of algae

An abundance of algae is generally a sign of water pollution or an unhealthy ecosystem, not purity. This condition, known as eutrophication, often occurs when excess nutrients (usually from fertilizers or waste) enter a water body, leading to an overgrowth of algae. Algal blooms can deplete oxygen levels in the water, harm aquatic life, and reduce water quality, which are indicators of environmental degradation rather than purity.

On the other hand, the other signs listed:

B.Abundance of small ...