First of all you should recall conditions for distortionless transmission. You can consider two approaches to this problem:
a) in time domain
Transmission of x(t) signal is distortionless if the output signal y(t) is defined by:
y(t) = Cx(t - to)
b) in frequency domain
For transmission through the system without distortion the frequency response of the system must satisfy two conditions:
|H(jw)| = C, and arg{H(jw)} = -wto
where:
w = omega
Now I think You are able to give answer for your question by yourself.
PS. If You want to know a little more You can study chapter 8.2 Haykin's "Signals and Systems" book.