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The signal $\cos \omega_{c} t+0.5 \cos \omega_{m} t \sin \omega_{c} t$ is

1. $\mathrm{FM}$ only
2. $\mathrm{AM}$ only
3. both $\mathrm{AM}$ and $\mathrm{FM}$
4. neither $\mathrm{AM}$ nor $\mathrm{FM}$