Which of the following is a standard IEEE 1394 transmission speed?

While 100 Mbps is a standard IEEE 1394 speed, the question asks for 'a standard' speed, and 400 Mbps is also a correct and commonly cited standard speed.

IEEE 1394, in its initial specification (FireWire 400), offered standard data transfer rates of 100 Mbps, 200 Mbps, and 400 Mbps. The 400 Mbps speed was widely adopted and is a common characteristic of FireWire 400 devices.

480 Mbps is a standard transmission speed for USB 2.0 (High-Speed USB), not IEEE 1394.

1000 Mbps (1 Gigabit per second) is typically associated with Gigabit Ethernet or later USB specifications, not the primary IEEE 1394 standards (though FireWire 800 reached 800 Mbps).