For each of the positive edge-triggered J-K flip flop used in the following future, the propagation delay is $$\Delta $$T

Which of the following waveforms correctly represents the output at Q₁?

The following binary values were applied to the X and Y inputs of the NAND latch shown in the figure in the sequence indicated below: X=0, Y=1; X=0, Y=0; X=1, Y=1. The corresponding stable P, Q outputs will be

For the circuit shown, the counter state (Q₁ Q₀) follows the sequence

Two D-flip-flops, as shown below, are to be connected as a synchronous counter that goes through the following Q₁Q₀ sequence $$00 \to 01 \to 11 \to 10 \to 00 \to ......$$
The inputs D₀ and D₁ respectively should be connected as