Which of the following is classified as a type of aggregate?

Gravel is classified as a type of aggregate because it consists of particles ranging from granular to boulder-sized, which are used in construction and civil engineering projects, particularly in concrete and asphalt mixes. Aggregates serve as a key component that provides strength, stability, and durability to the resulting mixture.

Topsoil, while it may be used in specific landscaping applications, is primarily composed of organic matter and nutrients aiding plant growth, rather than functioning as a structural component in construction. Water is a vital component in many construction processes, especially in mixing concrete, but it is not an aggregate. Cement, although crucial for bonding aggregates together to form concrete, is a binder material and not classified as an aggregate itself.

Therefore, gravel stands out as the correct choice due to its primary role as a structural element in various construction materials.