Correct Option: B

The given modulated wave.
S(t) = (2.5 + 5 cos ω_mt) cos ω_ct
or S(t) = 2.5 (1 + 2 cos ω_mt) cos ω_ct …(i)
The method for detecting a modulated signal will depend upon the modulation index, μ.
On comparing equation (i) with the standard equation
S(t)=Ac(1 + μ cos ω_mt) cos ω_c t …(ii)
we get
μ = 2, shows a over modulation case.
So in this case overmodulated signal can be recovered using a costly as well as complex technique i.e. synchronous detection.