Which of the following is a man-made signal?

Modulation is a process of superposing

The process of the loss of strength of a signal while propagating through a medium is known as:

Indicate which one of the following systems is digital.

For an amplitude-modulated wave, the audio frequency is $500 \, \text{cycles/second}$. What is the actual carrier frequency in $\text{cycles/sec}$?

The bit rate for a signal,which has a sampling rate of $8 \, kHz$ and where $16$ quantisation levels have been used,is ......... $bits/sec$.