The weight of the T-6B canopy is counterbalanced by ________ during opening/closing operations.

The weight of the T-6B canopy is counterbalanced by oil-filled struts during the opening and closing operations. These struts utilize hydraulic fluid to create a cushioning effect, allowing the canopy to open and close smoothly while providing support against its weight. As the struts compress when the canopy is closed, they help to counteract the gravitational force acting on the canopy, making it easier to operate. This design ensures that the canopy can be handled with relative ease by the pilot or ground crew, enhancing safety and efficiency during pre-flight and post-flight operations.

Other options like pneumatic cylinders and mechanical counterweights serve different functions or do not apply to the specific mechanism used in the T-6B's canopy system. Electrical clutches, while useful in other contexts, are not involved in the canopy operations, thus aligning the function to the oil-filled struts specifically as the correct choice.