The STEP POINT displays the computed ETA at, and distance to, the first possible step climb point based on gross weight. The STEP button (1R) is then used to enter step climb or step descent altitudes for crew evaluation. It is blank when within ___ NM of top of descent or when RTA mode is active.
A.A.100
B.B.50
C.C.30
D.D.10
正确答案是A