Explanation:

Limestone regions are marked by landforms like sinkholes, swallow holes, underground caves etc. which are an outcome of “Solution”. The calcium carbonate in limestone dissolves under the chemical impact of carbonic acid (formed by mixing of rain water with atmospheric carbon dioxide).
Arid regions are primarily marked by mechanical weathering by wind action
Glacier regions are also marked by physical weathering features like cirques, pyramidal peaks, moraines etc.
Humid regions exhibit both physical (like wetting and drying) and chemical weathering (like oxidation) but physical weathering dominates.