Final answer:
Option 'b. English soccer fans cheering on their national team in the World Cup' exemplifies a centripetal force, which is a force that unites a nation or group.
Step-by-step explanation:
The question seeks to identify which option would best be characterized as a centripetal force. Centripetal forces are those that act to unify a nation or group, leading to agreement, nationalism, and cohesion. Key examples of such forces include ethnic unity, social/economic equity, and shared nationalism after events that rally a country together, like the unity seen in the U.S. after the 9/11 attacks.
Considering the provided options and understanding of centripetal forces, answer 'b. English soccer fans cheering on their national team in the World Cup' perfectly exemplifies a centripetal force. This is because it represents a situation where people are united in support of a common cause, which in this case is their nation's success in an international competition. The other options signify division or conflict, hence exemplifying centrifugal forces instead.