Final answer:
Without additional context, no definitive choice can be made about the correct model for pollution removal from a lake as described by f(r). Further information on the specific dynamics of the pollution removal process is necessary to determine the correct mathematical representation.
Step-by-step explanation:
The question asks about the correct representation of pollution removal from a lake at a rate of f(r) kg/day on day r. The four options provided represent different mathematical models for this rate of pollution removal. However, without further information about the way the pollution removal process changes over time, it is impossible to definitively choose which option is correct. More context is required to determine whether the rate is constant, increases with time, decreases with time, or has another relationship to time. Additional data on pollution levels, the specific methods used for removal, and environmental factors would inform the appropriate model. The ideal answer should reflect real-world pollution removal dynamics and be consistent with the units of kg/day.