Cement is a mixture of:
A. calcium silicates
B. calcium aluminates
C. calcium silicates and aluminates
D. none of these

Hint:Cement is a binding substance that is used for the construction purposes that sets, hardens, and adheres to other materials to bind them together. Cement is solely used on its own but rather to bind/ aggregate sand and gravel together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete.

Complete step by step answer:
The most common cement used around the world is the Portland cement which comes under the category of hydraulic cement. This cement is made by heating limestone (calcium carbonate) with other materials (which contains $26\% $ of dicalcium silicate ($C{a_2}Si{O_4}$ ), $51\% $ of tricalcium silicate ($C{a_3}Si{O_5}$ ) and $11\% $ of tricalcium aluminate ($C{a_3}A{l_2}{O_6}$ ) to \[1,450\;^\circ C\] in a kiln, under a process which is known as calcination that generally liberates a molecule of carbon dioxide from the calcium carbonate to yield calcium oxide or quicklime, which then chemically combines with the other materials in the mix to form calcium silicates, calcium aluminates and other cementitious compounds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make ordinary Portland cement, the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient of concrete, mortar, and most non-specialty grout.

Thus, the correct option is C. calcium silicates and aluminates.

Note:The most common use of cement is to make concrete. Concrete is a complex material which is made up of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape, and once it hardens, can be a structural (load bearing) element. Due to the immense strength of concrete, it becomes the major component of the pillars that we find in the buildings.