Being a biology student , you have noticed that ponds and lakes near by your crop field are over crowded with algae and other aquatic plants , lead to water pollution . how do this occur and how to solve this problem?

This is very easy, since the lakes are near a crop field, runoff fertilizers have obviously contaminated the water, and to prevent it : Careful contouring of the land can help prevent this by slowing and spreading the flow of water, giving it time to soak in before it runs downhill. Terraces, swales and buffer zones can be used to keep fertilizer from entering ponds and other waterways. That was from google for a more detailed response.

Hope this helps, if not, comment below please

oak trees? ? what was listed

"d.) carbon dioxide and hydrogen sulfide"