# Attenuation is

$\begin{array}{1 1}(a)\;\text{Loss of strength of signals during propagation}\\(b)\; \text{Modulation of the signal}\\(c)\;\text{Demodulation of the signal}\\(d)\;\text{Amplification of the signal}\end{array}$

Attenuation is loss of strength of signal while propagating through the medium.
Hence (a) is the correct answer.