When a speed adjustment is necessary to maintain separation, what minimum speed may ATC request of a arrival aircraft operating below 3,000 meters?
A.Turbojet aircraft, a speed not less than 230 knots. Piton engine and turboprop aircraft, a speed not less than 150 knots.
B.a speed not less than 210 knots; except 20 miles from threshold, not less than 170 knots. Piston and turboprop aircraft. not less than 200 knots; except 20 flying miles from threshold, not less than 150 knots.
C.Not less than 250 knots
正确答案是B