The DME in an aircraft, cruising at FL210, fails to achieve a lock on a DME at MSL at a range of 210nm. The reason for this is:
a. The beacon is saturated
b. The aircraft is beyond the maximum usable range for DME
c. The aircraft is beyond line of sight range
d. The aircraft signal is too weak at the range to trigger a response
a. The beacon is saturated
b. The aircraft is beyond the maximum usable range for DME
c. The aircraft is beyond line of sight range
d. The aircraft signal is too weak at the range to trigger a response