Final answer:
Option (b), Scholar Robert Putnam and others argue that social capital in the United States is decreasing, which may detrimentally affect political participation and community involvement.
Step-by-step explanation:
Regarding social capital in the United States today, the belief that it is decreasing is supported by the work of scholars such as Robert Putnam. Putnam argues that social capital, which refers to the collective value of all 'social networks' and the inclinations to do things for each other that these networks foster, has declined. This decline is linked to a decrease in membership in small, interactive groups and, therefore, a reduction in the willingness and ability of individuals to engage in representative government.
Political participation is encouraged by social capital because it reinforces social bonds and networks that can lead to increased communal involvement and civic engagement. However, some have countered this perspective by pointing out that while certain forms of social participation, like bowling leagues, have declined, others, such as soccer leagues, have risen. Additionally, technology has been argued to increase connectedness, though there is debate about the depth of these online connections compared to in-person ones.
Summing up, social capital plays a substantial role in encouraging political participation and community involvement, but there is no consensus on whether social capital has been increasing, decreasing, or remains constant in the United States today, as different data and methodologies can lead to varying conclusions.