Ballast shaping
Answer: b

Bulldozers are generally suitable for subgrade construction, foundation pit excavation, site leveling, tree removal, stone slag collection, etc. , and can loosen the soil for scrapers and excavators, and help shovel and pull various traction working devices.

Scrapers are mainly used for medium-distance large-scale earthwork transfer projects.

Excavation machinery is mainly used for earthwork excavation and loading.

Graders are mainly used for leveling subgrade and crushed stone pavement, site shaping and peaceful operation in earthwork, and can also be used for trimming subgrade cross section, scraping embankment and cutting slope, and excavating side ditches and road troughs.