Which of the following phone emissions uses the narrowest bandwidth?

Standard amplitude modulation (AM) transmits a central carrier along with two identical sidebands containing the audio information. Single sideband (SSB) improves efficiency by suppressing the carrier and eliminating one of the sidebands, leaving only one sideband to be transmitted. Because it only transmits half of the AM signal footprint, SSB requires exactly half the bandwidth of standard AM, typically utilizing only 2.4 to 3 kHz for standard voice communications. This makes it highly efficient for amateur bands where space is limited. In contrast, frequency modulation (FM) and phase modulation (PM) signals naturally swing across a much wider range of frequencies, typically occupying 10 to 15 kHz of bandwidth. Vestigial sideband is a technique formerly used for analog television broadcasting and is exceptionally wide.