The correct answer is: A. Lime and silica.
Portland cement is a binder, a substance used to bind other materials together. It is the most common type of cement in general use and the basic ingredient of concrete, mortar, and stucco. Portland cement is made by heating limestone and clay to very high temperatures. The resulting clinker is then ground into a fine powder and mixed with gypsum.
The main ingredients of Portland cement are lime and silica. Lime is a calcium-based compound, while silica is a silicon-based compound. These two compounds react together to form calcium silicate, which is the main component of Portland cement.
Other ingredients in Portland cement include alumina, iron oxide, and magnesia. These compounds are present in smaller amounts, but they play an important role in the properties of Portland cement.
Alumina is a aluminum-based compound. It helps to improve the strength of Portland cement.
Iron oxide is a iron-based compound. It gives Portland cement its characteristic color.
Magnesia is a magnesium-based compound. It helps to improve the workability of Portland cement.
The properties of Portland cement can be modified by adding different amounts of these other ingredients. For example, adding more alumina will make Portland cement stronger, while adding more iron oxide will make it more durable.