Encoder and My Challenges on Digital Logic

Question

in following Encoder, the priority of bigger number is bigger. if the initial state is 0, after how many clock pulse, Q after being 1, change states to zero.

My professor, say (3), why ?

Answer 1

At initial state: Q = 0, D1D0 = 00, Q' = 1, JK = 00 encoder input:0001

After 1st clock pulse,

D1D0 = 01 encoder input:0011 so JK =01 resets output Q = 0, Q' =1

After 2nd clock pulse,

D1D0 = 10 encoder input:0101 So JK =10 sets output Q = 1, Q' =0

After 3rd clock pulse,

D1D0 = 11 encoder input:1110 So JK = 11. toggles the output.

or Q switches from 1 to 0.