With the autopilot engaged in the V/S mode during a climb, how can the autothrottle operate?

In the context of autopilot operation during a climb in Vertical Speed (V/S) mode, the autothrottle can indeed function in the SPEED mode, which maintains a constant indicated airspeed (IAS). When the autopilot is set to V/S mode, it is focused on controlling the vertical speed of the aircraft. For efficient climb performance, the autothrottle system can be used to adjust engine power to achieve and maintain the desired IAS appropriate for the climb.

Operating in the SPEED mode allows for a better balance between climb rate and airspeed stability, especially since the aircraft's performance will depend on both the vertical speed and the airspeed. Maintaining a specific IAS is important to ensure the aircraft stays within optimal performance parameters, avoiding stalls or excessive drag.

The other options discuss states that do not accurately reflect how the autothrottle can be utilized during such operating conditions. Autothrottles are designed to support optimal flight operations, and in climb situations where V/S is selected, it is critical for the pilots to control the airspeed effectively, thus reinforcing the correctness of this answer.