Waveform A starts at Vss then goes to Vpp and ends with Vss with pulses between V4 and V1 every clock pulse, whereas waveform B has the same level across the duration of a frame with start and end pulses varying every second frame.
Also, pulse duration in waveform A is 1/2 (200 clock impulses) of the waveform B (400 clock impulses) ..