Final answer:
Similarity in hobbies and interests is most likely to form a basis for cross-ethnic group friendships, as common activities provide a platform for shared experiences and connections.
Step-by-step explanation:
The question is about what similarity is most likely to serve as a basis for cross-ethnic group friendships. From a sociological point of view, the answer is hobbies and interests. The concept of homophily suggests that people tend to form social networks with others who are similar to them in various aspects. However, shared hobbies and interests can bridge the gap between different ethnic backgrounds, providing a common ground for friendships to develop. Mutual interests in activities allow individuals to engage in shared experiences, regardless of their ethnicity, which can lead to stronger and more meaningful connections.