General exam question G6A12

WhyThe primary purpose of a screen grid in a vacuum tube is to reduce grid-to-plate capacitance. A screen grid, held at a steady positive voltage between the control grid and plate, electrostatically shields the control grid from the plate, which greatly reduces the grid-to-plate capacitance that would otherwise cause unwanted feedback in an RF amplifier stage, answer A. It isn't primarily there to boost efficiency, increase the control grid's resistance, or lower plate resistance, those aren't the screen grid's defining role.