At the first stage in the production of cement, limestone and clay (34-crush)____________ to form a powder. This powder then (35-mix)______________ before it passes into a rotating heater. After heating, the resulting mixture (36-grind)_______________, and cement (37-produce)______________. Finally, the cement (38-package)_______________in large bags.
 
Cement is one of the four raw materials that (39-use)_______________ in the production of concrete, along with gravel, sand and water. To be exact, concrete (40-consist)_______________ of 50% gravel, 25% sand, 15% cement and 10% water. All four materials are blended together in a rotating machine called a concrete mixer.