An incoming bit stream is partitioned into an even stream and an odd stream in which of the following digital modulation systems?

In a coherent M-ary system, the phase difference between symbols plays a crucial role in representing information. Compared to coherent binary phase shift keying (BPSK), what potential advantage does a coherent M-ary scheme offer?

If the binary sequence '1100' is encoded using the NRZ-L (Non-Return-to-Zero Level) encoding method, how many signal level transitions occur within the sequence duration (excluding the initial transition at the start of the first bit)?