Step 1: Contrast rural with urban society:
Sociology textbooks typically contrast homogeneous, close-knit rural communities with heterogeneous, anonymous urban ones.
Step 2: Apply the contrast to the options:
Caste system, primary relationships and nature-dependence all fit the rural profile; "heterogeneous population" fits the urban profile instead, making it the feature that does NOT belong to rural society.
Final Answer:
Heterogeneous population (Option B)