The correct answer is B) reducing the quantity of lubricant until only a mist of oil is present on the ball bearings. As the speed of an oil-lubricated ball bearing increases, the fluid friction due to churning generates excessive heat. This heat can be avoided by reducing the quantity of lubricant to the minimum amount necessary, which is a mist of oil on the ball bearings. This reduces the churning and associated heat generation, while still providing adequate lubrication. The other options are incorrect because: A) adding more lubricant would increase the churning and heat generation; C) maintaining a continuous fluid level over half the outer race may still result in excessive churning; and D) installing oil rings does not address the underlying issue of excessive lubricant causing heat generation.