Final answer:
The described organism is a ciliate protozoan that moves with cilia and ingests bacteria by endocytosis, matching the characteristics of Paramecium, which makes A) Protozoan the correct answer.
Step-by-step explanation:
The organism described in the question is a motile unicell that lives in pond water, is covered with cilia, swims very fast, and ingests food by endocytosis. These characteristics align with a group of protists known as ciliates, which use their cilia to coordinate directed movements and ingest food particles. Moreover, they use a specialized structure, the oral groove, to facilitate the ingestion of bacteria, leading to the formation of food vacuoles where digestion occurs. A well-known example of a ciliate is the Paramecium, which exhibits this type of locomotion and feeding method. Therefore, the correct answer to the question is A) Protozoan