ILIST - II'V' shaped valleyRiver EROSION'U' shaped valleyGlacial erosionSink holesKarst topographyYardangsWind erosionHence, option 2 is correct.'V' shaped valley:A V-valley is formed by erosion from a river or stream over time.It is called a V-valley as the shape of the valley is the same as the letter “V”.As the river erodes downwards the sides of the valley are exposed to freeze-thaw weathering which loosens the rocks (some of which will fall into the river) and steepens the valley sides. 'U' shaped valley:U-shaped valleys, trough valleys, or glacial troughs, are formed by the process of glaciation.They are characteristic of mountain glaciation in particular.They have a characteristic U shape in cross-section, with steep, straight sides and a flat or rounded bottom.Sinkholes:Sinkholes are depressions formed in the ground when layers of the Earth's surface start collapsing into caverns. They can occur SUDDENLY and without warning, because the land under the surface of the Earth can stay intact for a period of time until the spaces get too big.Yardangs:Wind abrasion excavates the bands of softer rocks into long, narrow corridors, separating the steep-sided, over-hanging ridges of hard rocks, called yardangs.They are formed by wind erosion through the abrasion process.Yardangs are PARALLEL troughs cut into softer rock RUNNING in the direction of the wind, separated by ridges.The direction of the yardangs can indicate the direction of the prevailing wind.