Limestone can be easily affected by which processes?

Correct answer: Carbonation and solution

The direct answer is C, carbonation and solution. Limestone is mainly calcium carbonate. When rainwater absorbs carbon dioxide from the air and soil, it forms weak carbonic acid. Step by step: rainwater takes in carbon dioxide; weak carbonic acid forms; this acidic water enters cracks in limestone; calcium carbonate dissolves gradually; cracks may enlarge into caves, underground channels, sinkholes, and other karst features. Option C is correct because carbonation helps the water dissolve limestone, and solution is the actual dissolving process. Option A is wrong because earthquakes and tsunamis are sudden tectonic or marine hazards, not the usual chemical weathering processes that dissolve limestone. Option B is wrong because air pressure alone does not explain limestone dissolution. Option D is wrong because magma flow is a volcanic process and is not required for ordinary limestone weathering. Other processes can affect limestone, but C is the specific and complete pair here. Memory cue: limestone plus weak carbonic acid means carbonation and solution, often producing karst.