The _ presents a uniform device-access interface to the I/O subsystem, much as system calls provide a standard interface between the application and the operating system.

a) Device drivers
b) I/O systems
c) Devices
d) Buses

Device drivers present a uniform device-access interface to the I/O subsystem.

They act as a bridge between the operating system and hardware devices, providing a standardized way for applications to interact with different types of devices. This abstraction layer simplifies the development of applications and makes the I/O subsystem more manageable.