34 According to 14 CFR part 107, what is required to operate a small UA within 30 minutes after official sunset?
C. Use of a transponder.
Transponders are heavy, power-hungry and ATC can't see them at low altitudes unless they are near an airport with radar service.
One of the reasons that controlled airspace usually begins at 500 ft is because ATC radar can't "see" transponder returns at low altitudes.
This is not the correct answer.