The real part of the propagation constant of a transmission line is :
reliability factor
phase constant
attenuation constant
stability constant
attenuation constant
Propagation constant 
Where,
Attenuation constant (real part)
Phase constant (imaginary part)
So, we can say from above
formula attenuation constant is the real part of propagation constant and phase
constant is the imaginary part of the propagation constant.
Hence, the correct option is
(C).
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