In amplitude modulation, the bandwidth of the signal is:

Solution

1. The frequency spectrum of an AM wave consists of $f_c-f_m$, $f_c$, and $f_c+f_m$.
2. The bandwidth is defined as the difference between the highest and lowest frequencies.
3. Bandwidth $$\begin{array}{rl}& =(f_c+f_m)-(f_c-f_m)\\ & =2f_m\end{array}$$.
4. Hence the answer is (C).