Answer:
Bacterial Population in the Water.
Step-by-step explanation:
First, let us define biotic factor. Biotic Factor is defined as "a living organism that shapes its environment."
In this case, look at the choices given.
"Bacterial population in the water": Compare the example to the definition. First, define:
1) Is a bacterial population considered to be a living organism?
2) Does bacterial population affect the populations of other species?
To answer the first question given, yes. Bacteria is considered to be a living organism. They are unicellular and typically move using a flagellum.
As of the second question, yes. Bacteria affects the populations of other species, whether as beneficial, or not. Typically, when we associate bacteria with humanity or the animal kingdom, we typically believe that bacteria's are harmful, but in reality, there are some beneficial bacterias. Bacterias found inside the gut usually are beneficial, such as probiotics or yeast, which help with the movement of the bolus from the mouth to the buttocks.
In the case of water-dwelling organisms, there are definitely bacteria populations, which may or may not be beneficial to the organisms living in the water. As long as they are only there for their purpose, then the bacteria is beneficial. However, if it spreads to a part of the body that does not need the bacteria, it is proven to be detrimental and must be exterminated from the area.
With this information, it is safe to say that A) Bacterial Population in the Water, is your answer.