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 churning of the lubricant can generate excessive heat, which can lead to premature bearing failure. To avoid this condition, it is recommended to reduce the quantity of lubricant until only a fine mist is present on the bearings. This reduces the amount of churning and minimizes the heat generation, improving the bearing's performance and lifespan. 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 would not be sufficient to prevent the churning and heat buildup. D) Installing oil rings on the ball bearings would not address the root cause of the excessive heat generation due to churning.