The collective control in a helicopter is utilized to:

The collective control in a helicopter is primarily utilized to change the angle of attack of the rotor blades, which directly influences the amount of lift generated. By pulling the collective control up, the pilot increases the pitch angle of all rotor blades simultaneously, thereby enhancing lift and allowing the helicopter to ascend. Conversely, lowering the collective reduces the pitch angle and decreases lift, resulting in descent. This mechanism is crucial for vertical flight, distinguishing it from fixed-wing aircraft that do not employ a collective control system for lift adjustment.

While adjusting altitude could be seen as a direct effect of using the collective, the specific function of the collective itself is tied to the angle of attack for lift generation. Likewise, controlling speed and yaw involves other helicopter controls such as the cyclic (for forward and lateral movement) and the tail rotor (for yaw), respectively. Therefore, the emphasis on the collective's role in adjusting the angle of attack is what makes it the most accurate choice in this context.