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A message signal given by
$m(t)=\left(\frac{1}{2}\right) \cos \omega_{1} t-\left(\frac{1}{2}\right) \sin \omega_{2} t$
is amplitude-modulated with a carrier of frequency $\omega_{c}$ to generate
$s(t)=[1+m(t)] \cos \omega_{c} t$

What is the power efficiency achieved by this modulation scheme ?

1. $8.33 \%$
2. $11.11 \%$
3. $20 \%$
4. $25 \%$