The correct answer is: B. Algae and aquatic plants.
Eutrophication is the process by which an aquatic ecosystem becomes enriched with nutrients (particularly phosphorus and nitrogen), leading to excessive plant growth and, consequently, depletion of oxygen in the water. This can lead to the death of fish and other aquatic organisms, and can make the water uninhabitable for humans and other animals.
Algae and aquatic plants are the primary cause of eutrophication. When these plants grow too quickly, they can form dense mats that block sunlight from reaching the bottom of the water. This prevents other plants from growing, and can also suffocate fish and other organisms that live on the bottom. In addition, the decomposition of dead algae and plants can use up oxygen in the water, leading to hypoxia.
Bryophytes, gymnosperms, and pteridophytes are all types of plants, but they do not contribute to eutrophication in the same way as algae and aquatic plants. Bryophytes are small, non-vascular plants that do not produce flowers or seeds. They typically grow in moist, shady environments, and do not have a significant impact on water quality. Gymnosperms are a group of plants that includes conifers, such as pines and firs. They produce seeds in cones, and their roots do not absorb as much phosphorus and nitrogen from the soil as the roots of other plants. Pteridophytes are a group of plants that includes ferns. They have vascular tissue, but they do not produce flowers or seeds. Their roots do not absorb as much phosphorus and nitrogen from the soil as the roots of other plants.
In conclusion, the correct answer is: B. Algae and aquatic plants.