ANS:C - tube mill

Cement clinker is reduced to a fine size primarily by a ball mill.

Explanation:

• Ball Mill: A ball mill is widely used in the cement industry for grinding cement clinker into fine powders. It operates by rotating a cylinder with steel grinding balls, causing the balls to fall back into the cylinder and onto the material to be ground. The rotation of the cylinder and the grinding action of the balls crush and grind the clinker particles into a fine powder.
• Roll Crusher: Typically used for secondary or tertiary crushing of materials, including some applications in cement production, but not specifically for reducing clinker to fine size.
• Tube Mill: Used for grinding various materials, including cement clinker, where the grinding occurs inside a rotating tube with balls or rods.
• Hammer Mill: Generally used for coarse grinding of materials, such as grains or biomass, but not typically used for reducing cement clinker to fine size.