Concept:The main idea is identifying a common geographic or human characteristic shared by all three places.
Explanation:Hong Kong, Java, and Manhattan are each small in area but have very large populations.
This gives them extremely high population density.
Rapid industrial growth applies to some of them, but not equally to all.
Multi-racial communities are present, yet they are not the defining shared feature.
High military technology is not a characteristic of these places.
Therefore, the common feature is high population density.
Answer:C. high population density