E8C13:What is described by the constellation diagram of a QAM or QPSK signal?

Direct answer summary (2024-2028 NCVEC pool)

The official correct answer for E8C13 is The possible phase and amplitude states for each symbol.

The key fact is The possible phase and amplitude states for each symbol. Match that fact to the exact condition in the question; the other choices describe a different rule, band, component, or operating situation.