Correct choice is (b) Multiplication in the time domain by a complex sinusoid
Best explanation: If x(t) and y(t) are two periodic signals with coefficients Xn and Yn,
Then y(t)= e^jmwtx(t)↔Yn=Xn-m.
Hence, we can see that a frequency shift corresponds to multiplication in the time domain by complex sinusoid whose frequency is equal to the time shift.