Which among the following is NOT an identity?

A

$$\sin 2\theta = 2 \sin \theta \cos \theta$$

B

$$\sin^2 \theta - \cos^2 \theta = 0$$

C

$$\cos 2\theta = \cos^2 \theta - \sin^2 \theta $$

D

$$\tan 2\theta = \frac{2 \tan \theta}{1 - \tan^2 \theta}$$