The correct answer is: a) Sand and gravel.
Sand and gravel are essential materials for construction. They are used in concrete, asphalt, and other building materials. They are also used in landscaping and erosion control.
Bauxite is a mineral ore that is used to produce aluminum. It is not a major construction material.
Coal is a fossil fuel that is used to generate electricity. It is not a major construction material.
Uranium is a radioactive metal that is used to produce nuclear energy. It is not a major construction material.
Sand and gravel are found in deposits all over the world. They are mined from open-pit or underground mines. The sand and gravel are then crushed and sorted by size. They are then washed and dried before being shipped to construction sites.
Sand and gravel are essential materials for construction. They are used in concrete, asphalt, and other building materials. They are also used in landscaping and erosion control.