Final answer:
Supporting the legislation requiring the use of bicycle helmets is an example of promoting the common good in community health nursing because it is a preventive health measure for the broader public's safety and wellbeing.
Step-by-step explanation:
An important philosophical value in community health nursing is to promote the common good. When considering which of the provided options exemplifies promoting the common good, we should recognize that the common good involves practices or policies that benefit the entire community, not just individuals.
Treatment that is oriented towards individual persons, such as treating obesity on an individual basis (option A) or treating each client with diabetes as unique (option C), while important, do not directly address the broader community's wellbeing.
On the contrary, supporting legislation for the use of bicycle helmets (option D) is a clear example of promoting the common good, as it is a preventive health measure that benefits the general public by reducing the risk of head injuries across the community, thus exemplifying a commitment to public safety and health at the community level.