G1E10

Why should an amateur operator normally avoid transmitting on 14.100, 18.110, 21.150, 24.930 and 28.200 MHz?

1. AA system of propagation beacon stations operates on those frequencies
2. BA system of automatic digital stations operates on those frequencies
3. CThese frequencies are set aside for emergency operations
4. DThese frequencies are set aside for bulletins from the FCC

Pick an answer to check it.