B Why did this waveform produce a different output Qa and Qb

B) Why did this waveform produce a different output (Qa and Qb)?

Schematic: http://tech-uofm.info/fall_2016/TECH3232/Lab8_sch.pdf

Solution

I belive its Out come of postive edge trigger D-flipflop where Qa its change with respect to input d,when ever the edge of clock signal change from 0 to1; where Qb its reset after evry rising edge of clock pulse.