Which of the following is a digital communications mode?

All the options listed are valid digital communications modes used in amateur radio. Packet radio is a legacy digital mode that transmits data in discrete blocks or "packets," forming the basis of systems like APRS. FT8 is a highly popular, modern digital mode designed specifically for weak-signal communication and rapid, automated contacts. IEEE 802.11 is the technical standard for Wi-Fi. Hams frequently use modified Wi-Fi equipment on amateur microwave bands to create high-speed digital mesh networks (such as AREDN). Because all three are valid, the correct answer encompasses all of them.