Escape (Or Back Door) in Application I/O Interface

Multiple Choice

Escape (or back door) in application I/O interface

A) allows a user to interrupt a device at any time.
B) allows access to a few additional devices, such as a time-of-day clock and a timer.
C) transparently passes arbitrary commands from an application to a device driver.
D) enables managing of devices with widely varying speeds ranging from a few bytes per second to gigabytes per second.