Identify the function which represents a periodic motion

The function is said to be periodic if we can write it in to form of, $y = Asin\left(\omegat + ϕ\right)$.

In the above options only we can write, $\sin \left(\omegat\right) + \cos \left(\omegat\right)$, in the form of, $sin$\left(\omegat\right)cos$\left(\dfrac{\pi}{4}\right) + \cos \left(\omegat\right)\sin \left(\dfrac{\pi}{4}\right) = 1 \times \sin \left(\omegat + \dfrac{\pi}{4}\right)$, so we can say that, $\sin \left(\omegat\right) + \cos \left(\omegat\right)$ is a periodic function.