Which of the following landforms is formed by the action of glaciers?

Glacial erosion is a mechanical process: a moving mass of ice, embedded with rock debris, scours and plucks the bedrock beneath and beside it as it flows downslope, producing distinctly rounded, broad, trough-shaped erosional landforms — unlike the narrower, sharper forms cut by flowing water.

A valley glacier moving through a pre-existing river valley widens and deepens the valley floor and steepens its sides through abrasion (embedded rock debris grinding against bedrock) and plucking (freeze-thaw action prying loose blocks of rock). This produces a broad, flat-floored, steep-sided trough with a distinctive rounded cross-section — the 'U' shaped valley.

• Lapies — Lapies are grooved, fluted limestone surfaces produced by the chemical dissolution (solution weathering) of rock by acidic rainwater — a karst process, unrelated to the mechanical scouring of moving ice.

• 'V' shaped valley — A 'V' shaped valley is cut mainly by a river's vertical downcutting into its bed, producing a narrow, steep-sided channel — a fluvial process, distinct from the broad lateral erosion of glacial ice.

• Waterfall — A waterfall forms where a river's course meets an abrupt break of slope or a band of harder, more resistant rock, causing a sudden vertical drop — this results from differential fluvial erosion, not from glacial action.

Among the given landforms, only the 'U' shaped valley is produced by the direct erosional action of glaciers.