Which command is used to configure an interface to use a specific clock rate?

The command to configure an interface to use a specific clock rate is "clock rate bits-per-second." This command is essential for serial interfaces, especially when configuring point-to-point connections where one end of the link may need to define the clocking, normally in the case of DCE (Data Communications Equipment) devices.

When you enter this command, you specify the clock rate in bits per second, which tells the router how fast to send data over the serial link. Without setting the clock rate on one of the devices connected via a serial link, communication may not occur effectively, as both devices must agree on the timing of data transmission.

The other options do not represent valid commands in Cisco IOS for setting the clock rate, which clarifies that "clock rate bits-per-second" is indeed the correct choice for this configuration task.