A bog is a wetland that receives its water primarily from:

Concept

Bogs are ombrotrophic, peat-forming wetlands: their water and dissolved nutrients come mainly from atmospheric precipitation.

Unlike fens, bogs are isolated from significant groundwater or surface-water inflow; this hydrology helps make them acidic and nutrient-poor.

Application

Among the listed sources, rainfall is atmospheric precipitation. Therefore, rainfall is the intended answer.

Contrast

• Nearby water bodies provide surface-water inflow and may carry dissolved minerals from the surrounding landscape.

• Melting snow or ice produces seasonal meltwater, not the defining atmospheric supply of a bog.

• The sea supplies saline water to coastal wetlands, whereas bogs are freshwater peatlands.

Cross-check

A bog–fen comparison gives the same result: bogs depend on precipitation, while fens receive groundwater or drainage through mineral soils.

Result

The intended answer is rainfall.