Degree of $(y^{\prime\prime})^2(y^\prime)^2=x\sin(y^\prime)$

Question

Degree of $(y^{\prime\prime})^2(y^\prime)^2=x\sin(y^\prime)$

My try: since the highest order derivative is $y^{\prime\prime}$ and it's raised to power $2$, therefore I think that degree should be $2$.

But in my assignment the answer is given that since $\sin(y^\prime)$ would contain increasing powers of $y^\prime$, therefore degree isn't defined.

Whose answer is correct?

Regards