Which of the following is a characteristic of direct law?

Direct law is a mode of flight control in the A320’s fly-by-wire system characterized by the absence of flight envelope protections. In this mode, the control laws directly translate the pilot's inputs into aircraft responses without any automation or limiting protections, such as those that prevent the aircraft from exceeding certain critical parameters.

This means that while flying in direct law, pilots have full authority over the aircraft's control surfaces and can maneuver it as they wish, which can be crucial in specific flight conditions or emergencies. The lack of protections can allow for a more intuitive piloting experience but also increases the risk since the aircraft can be pushed beyond its safe operating limits if the pilots are not careful.

The other options present elements pertaining to the aircraft's operation but do not accurately reflect the defining characteristics of direct law. The requirement to fly with autopilot on, the command of a roll rate by the sidestick, and the necessity of manual gear extension do not align with the core principles that define direct law.