answer is D
if x=1 then $0\rightarrow 1\rightarrow 3\rightarrow 0\rightarrow 1\rightarrow 3\rightarrow 0\rightarrow 1\rightarrow 3............$
if x=0 then $0\rightarrow 1\rightarrow 3\rightarrow1\rightarrow 3\rightarrow 1\rightarrow 3\rightarrow $
one thing we should note is that
after a few clock cycle
means at x=0 after few clock cycle it will move from 1 to 3 ,3 to 1,1 to 3 .........................