Final answer:
Building tunnels, bridges, flattening hills, and filling hollows are environmental modifications made in order to construct large engineering projects, particularly in the field of civil engineering.
Step-by-step explanation:
Building tunnels, bridges, flattening hills, and filling hollows are environmental modifications made in order to construct large engineering projects. These modifications are commonly made in the field of civil engineering, which involves the design and construction of infrastructure such as roads, bridges, dams, and buildings. These modifications are necessary to overcome natural obstacles and create a stable foundation for the structures. For example, tunnels are built through hills or mountains to create a passage for roads or rail lines, bridges are constructed over bodies of water, and hills are flattened and hollows filled to create a level surface for construction. These modifications require careful planning, surveying, and engineering calculations to ensure the safety and stability of the structures.