Final answer:
The answer to the question is option C. Achievable standards. These standards denote the level of quality that can be reached under the best conditions and serve as reference points for evaluation.
Step-by-step explanation:
The answer to the given question is option C. Achievable standards. Achievable standards denote the level of quality that can be reached under the best conditions, typically conditions similar to those under which efficacy is determined. These standards serve as reference points and can be used as benchmarks for evaluation. For example, in the field of water quality, the US Environmental Protection Agency (EPA) has established water quality standards to protect human health and the environment. These standards define the goals for a body of water and specify its uses, as well as establish criteria to protect those water uses and requirements to protect water from pollutants.