Question id 399 - Preflight Preparation - FAA PPL(A) - Private Pilot Airplane

Preflight Preparation - (Refer to figure 20, area 5.) The CAUTION box denotes what hazard to aircraft?
Unmarked balloon on cable to 3,008 feet MSL
Unmarked balloon on cable to 3,008 feet AGL.
Unmarked blimp hangers at 300 feet MSL

Training tests and timed exam simulations FAA PPL(A) - Private Pilot Airplane