Which of the following types of signal has the narrowest bandwidth?

Continuous Wave (CW), the mode used for transmitting Morse code, consists of simply turning a single radio frequency carrier on and off. Because it carries no complex audio, voice, or video data, it requires an extremely narrow bandwidth—typically only about 150 Hz. To put this in perspective, SSB voice requires about 3,000 Hz (3 kHz), FM voice uses 10,000 to 15,000 Hz, and video modes require even more. Because CW concentrates all of the transmitter's power into such a tiny sliver of spectrum, it is incredibly efficient and can be heard much further away than voice signals of the same power.