Final answer:
Big business owners are not typically considered part of the Democratic Party base today; this group often aligns more with the Republican Party due to its support for lower taxes and less regulation. While labor unions, environmentalists, and minority groups are often part of the Democratic Party base, big business owners are more likely to align with the Republican Party.
Step-by-step explanation:
The group that is not likely to be considered part of the Democratic Party base today is C) Big business owners. The Democratic Party typically attracts support from labor unions, environmentalists, and various minority groups due to their focus on social justice, labor rights, and environmental protection. Historically, big business interests often align more with the Republican Party, as they tend to support lower taxes and less regulation that can be beneficial for business growth and profits.