General exam question G8A06

WhyQPSK31 is sideband sensitive, its encoding provides error-correction-like redundancy, and its bandwidth is approximately the same as BPSK31. QPSK31 depends on which sideband it's demodulated relative to (making it sideband sensitive), its four-phase encoding scheme provides built-in error-correction-like redundancy that plain BPSK31 lacks, and its symbol rate, and therefore its occupied bandwidth, is essentially the same as BPSK31's since only the phase-state count differs, so all three statements are true, answer D. Since A, B, and C are each individually accurate, the complete answer has to include all of them.