Declines in mines are inclined tunnels primarily used for:

Solution (By Examveda Team)

A decline in mining is an inclined tunnel driven from the surface into the mine.
Declines are not exclusively used for a single purpose; they serve multiple functions in mine development.
Option A: Drainage only is incorrect. While declines can be used for drainage, this is not their primary purpose. Drainage is often a secondary benefit, or a consideration in their design and placement.
Option B: Hoisting ore is incorrect. While ore can *sometimes* be hoisted using a decline, it's far more common to use shafts or ramps for main ore hoisting because those structures can handle higher volumes and steeper angles efficiently. Declines are generally less efficient for large-scale ore transport.
Option C: Surface ventilation is incorrect. Ventilation is crucial for mine safety, but declines aren't primarily designed for this purpose. Ventilation is usually achieved through a combination of shafts, raises, and other ventilation openings specifically designed to create airflow throughout the mine.
Option D: Access by vehicles is the most accurate answer. Declines provide inclined access for vehicles (like trucks, loaders, or smaller personnel carriers) to transport personnel, equipment, and materials to and from the underground workings. This is their main function. The grade (slope) of the decline is designed to accommodate vehicles and their operational needs. A decline offers a more flexible and potentially less costly access solution compared to a vertical shaft which requires substantial infrastructure for hoisting and personnel transport.