Flight altitudes in the holding area: from 600m upward, there is a flight altitude for every 300m. The true height between the lowest holding altitude and the highest obstacle should not be less than _______ m, the true height between the lowest holding altitude and the initial altitude in an instrument approach should not be less than _______ m.
A.600, 300
B.300, 600
C.900, 600
D.600, 900
正确答案是A