RVR低于多少米时的运行就被称作是低能见运行？When it is called low visibility operatio

RVR低于多少米时的运行就被称作是低能见运行？When it is called low visibility operation，the RVR is lower than ?

A.400米。400m

B.500米。500m

C.550米。550m

正确答案是1