Which weathering process is more important in the early development of karst topography?

Correct answer: Carbonation and solution

Karst topography develops mainly in soluble rocks, especially limestone. Rainwater absorbs carbon dioxide from the air and soil, forming a weak carbonic-acid solution. This water enters cracks in limestone and dissolves the rock gradually. The process, called carbonation and solution, enlarges joints and openings and can begin the formation of caves, sinkholes, underground drainage, and related karst features.

Option B is correct because carbonation and solution are the characteristic early weathering processes in limestone karst. Salt crystallization, frost action, and thermal expansion can affect rocks in suitable environments, but they do not provide the main explanation for the initial development of typical limestone karst. The key relationship is soluble limestone plus weakly acidic water, which produces dissolution and underground drainage.