In which of the following is the remote sensing technique $NOT$ used?

The height of a $T.V.$ tower is $75 \ m$. What is the maximum distance in $km$ up to which $T.V.$ transmission can be received (in $.98$)? (Radius of the Earth $= 6.4 \times 10^6 \ m$).

In amplitude modulation,the amplitude of the $.......$ wave varies in proportion to the instantaneous value of the $.......$ wave.

$List-I$	$List-II$
$A.$ Facsimile	$I.$ Static Document Image
$B.$ Guided media Channel	$II.$ Local Broadcast Radio
$C.$ Frequency Modulation	$III.$ Rectangular wave
$D.$ Digital Signal	$IV.$ Optical Fiber

Choose the correct answer from the following options:

Radio waves of constant amplitude are produced by a/an . . . . . . .

If the frequencies of the carrier wave and message signal are $1 \text{ MHz}$ and $28 \text{ kHz}$ respectively,then the frequencies of the side bands are