Step 1: Understanding the Concept:
Structural and socioeconomic bottlenecks constrain farm equipment adoption among Indian smallholders.
Step 2: Detailed Explanation:
1. Small and fragmented landholdings (Statement A): Over $86\%$ of Indian operational holdings belong to small and marginal farmers ($< 2\,\text{ha}$), rendering ownership of heavy agricultural machinery economically unviable.
2. Inadequate institutional credit financing constraints (Statement B): High capital investment requirements coupled with limited access to affordable term loans restrict equipment acquisition.
Step 3: Final Answer:
Therefore, small farm holdings and credit unavailability (A and B only) represent the primary structural reasons.