Amplitude and Phase Distortion Signal

Find the output to each of the inputs given below. For which cases is the transmission
distortionless? For the other cases, indicate what type of distorsion in imposed.
(a) cos(48πt) + 5 cos(126πt)
(b) cos(126πt) + 0.5 cos(170πt)
(c) cos(126πt) + 3 cos(144πt)
(d) cos(10πt) + 4cos(50πt)
Solution: Note that the four input signals are of the form xi(t) = a cos(2πf1t)+b cos(2πf2t),
for i = 1, 2, 3, 4. Consequently, their Fourier transforms consist of four impulses:
Xi(f) = a/2[δ(f + f1) + δ(f − f1)] + b/2[δ(f + f2) + δ(f − f2)], i= 1, 2, 3, 4.
With this in mind, we have the following
(a) Amplitude distortion; no phase distortion.
(b) No amplitude distortion; phase distortion.
(c) No amplitude distortion; no phase distortion.
(d) No amplitude distortion; no phase distortion.

I've got the answer... as mentioned above..
However.. i just can't understand it..
should i calculate something to proof that the signal have amplitude or phase distortion?
please give me some idea to understand this question..

there is more to the question. "find the outputs" is the relevant part. As given, this makes no sense -- nothing is given to put this in context.