Final Answer:
Airspeeds of not less than b) 100 knots should be assigned to arriving reciprocating engine or turboprop aircraft operating below 10,000 feet.
Step-by-step explanation:
The assignment of airspeeds for arriving aircraft is a critical aspect of air traffic control to ensure safe and efficient operations. In this context, the appropriate airspeed for arriving reciprocating engine or turboprop aircraft operating below 10,000 feet is not less than 100 knots (Option B).
This guideline helps maintain proper separation between aircraft and facilitates a smooth and controlled flow of air traffic during the approach and landing phases. Options A (90 knots), C (110 knots), and D (120 knots) do not align with the specified requirement and may not provide the necessary safety margins or operational considerations for aircraft arriving in this category.
Option B is the answer.