according to given output wave form, o/p should be 1 between t$_0$ and t$_1$ only, remaining it is 0.
note that initially Q$_1$ = Q$_2$ = 0 ===> $\overline{Q_1}$ = 1
if you see the option c and option d,
Before applying the clock pulse, Q$_1$ = 0,
given that, always 1 is provided to the D$_1$-FlipFlop
==> after applying clock pulse, it never generate OUTPUT as 0.
∴ $\overline{Q_1}$ = 0 after applying first clock pulse !
===> After first clock pulse onwards D$_2$ = 0 ==> From second clock onwards Q$_2$ = 0
But we have to choose between c and d,
What is the difference between them ?
option c is " positive edge triggered " where option d is " negative edge triggered "
By seeing output waveform, output is raised at t$_0$ positive edge ==> option c is the answer !