Question

eutrophication...: helps to purify water is a natural process. is characteristic of lakes with few fish. happens when fertilizers enter natural waterways.

Explanation:

Step1: Define eutrophication

Eutrophication is the enrichment of water bodies with nutrients. It can be a natural, slow - occurring process as nutrients accumulate over time in water bodies (hence it is a natural process).

Step2: Human - induced factor

When fertilizers from agricultural fields or other sources enter natural waterways, they add excessive nutrients (like nitrogen and phosphorus) which accelerates the eutrophication process.

Step3: Analyze other options

Eutrophication does not help to purify water; instead, it can lead to water quality degradation. Also, while eutrophication can cause changes in fish populations, it is not characteristic of lakes with few fish in a defining way.

Answer:

B. Is a natural process., D. Happens when fertilizers enter natural waterways.