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

An amplitude modulated signal is plotted below. Which one of the following best describes the above signal?

We do not transmit low frequency signals to long distances because:
$(a)$ The size of the antenna should be comparable to signal wavelength,which is impractical for a signal of longer wavelength.
$(b)$ Effective power radiated by a long wavelength baseband signal would be high.
$(c)$ We want to avoid mixing up signals transmitted by different transmitters simultaneously.
$(d)$ Low frequency signals can be sent to long distances by superimposing them with a high frequency wave.
Therefore,the most suitable options are:

$A$ message signal is used to modulate a carrier signal of frequency $5 MHz$ and peak voltage of $40 V$. In the process,two side-bands are produced separated by $40 kHz$. If the modulation index is $0.75$,then the peak voltage and frequency of the message signal,respectively,are:

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

In an amplitude modulation,a modulating signal having amplitude of $X$ Volt is superimposed with a carrier signal of amplitude $Y$ Volt in the first case. In the second case,the same modulating signal is superimposed with a different carrier signal of amplitude $2Y$ Volt. The ratio of the modulation index in the two cases respectively will be: