平飞巡航时应定时交叉检查主高度表，正常情况两个主高度表读数差值不应大于? How much difference between the primary altimeters should be no more than when the flight crew crosscheck the primary altimeters every one hour in level flight cruise?
A.200英尺 200FT
B.150英尺 150FT
C.75英尺 75FT
正确答案是A