Explanation: Marker beacon systems transmit at 75 MHz with vertical polarization. Aircraft utilize a specialized receive antenna for these signals. A balanced loop antenna is commonly used because it is compact, low-profile, and can be mounted effectively on the aircraft's underside to efficiently receive the vertically polarized signals. Option A is incorrect as electronically steerable phased-array antennas are overly complex and expensive for a simple, fixed-frequency marker beacon receiver. Option B is incorrect because a folded dipole for 75 MHz would be relatively large and less practical for a dedicated aircraft installation compared to a compact loop. Option D is incorrect because marker beacon transmissions are vertically polarized, meaning the aircraft requires a vertically polarized receive antenna for optimal reception, not a horizontally polarized one.