Covers the accounting equation

When erosion narrows the neck of a meander and the river finally takes a straighter course, the former loop becomes separated from the main channel. The isolated, usually crescent- or horseshoe-shaped water body is called an oxbow lake, making option A correct. A lagoon is separated from the sea, a cirque lake is associated with glacial hollows, and a delta is sediment deposited at a river mouth.

A delta is a depositional landform that develops at a river mouth when the river enters a slower water body and loses carrying energy. Sand, silt, and clay settle there, often producing a roughly triangular plain crossed by distributary channels. Hence option A is correct. A cirque is glacial, a yardang is wind-eroded, and a sea cave is carved by waves along a coast.

An alluvial fan forms where a stream leaves a steep mountain valley and reaches flatter ground. The sudden decrease in slope and speed reduces the stream’s carrying capacity, so gravel, sand, and silt spread outward in a fan-shaped deposit. Thus option A is correct. A sea arch is wave-eroded, a glacial valley is ice-eroded, and a stalagmite grows upward from a cave floor.

An arete is a narrow, sharp-edged ridge produced when glaciers erode the mountain from two opposite sides, often between adjacent cirques or glacial valleys. This two-sided erosion leaves a knife-edge crest, so option A is correct. An oxbow lake is a cut-off river bend, loess is wind-blown silt, and a bar is a depositional ridge in water.

A glacial horn is a sharp, pyramidal mountain peak formed when several cirques erode backward from different sides of the same mountain. As the cirques enlarge, the intervening ridges become narrower until a pointed summit remains. Hence option A is correct. A meander and levee are river features, while a beach is a coastal depositional feature.

A hanging valley is a tributary valley whose floor lies above the floor of the main glacial valley. The main glacier usually has greater thickness and erosive power, so it cuts more deeply than the smaller tributary glacier. The height difference may produce a waterfall, making option A correct. A delta and floodplain are river depositional features, while a yardang is wind-eroded.

A moraine is an accumulation of rock fragments, sand, clay and other debris transported and deposited directly by a glacier. Because glacial ice carries material of many sizes without sorting it by water, moraine deposits are commonly unsorted. Therefore, option A is correct. A delta and spit are water-built deposits, whereas a sea cliff is an erosional coastal feature.

Glacial abrasion is the scraping, grinding and polishing of bedrock by rock fragments embedded in moving ice. As the glacier travels, these fragments act like sandpaper and may leave scratches or grooves called striations. Hence option A is correct. Meandering describes a river’s winding course, salinization is salt accumulation in soil, and condensation is gas changing into liquid.

A river terrace is a step-like bench representing an older floodplain left above the river’s present level. It forms when renewed vertical erosion, often caused by uplift or a fall in base level, makes the river cut downward into its valley. The former floodplain is abandoned as a terrace, so option D is correct. The other choices are wind, coastal and glacial features.

A stalagmite grows upward from the floor of a limestone cave. Water dripping from the roof carries dissolved calcium carbonate and leaves a small calcite deposit when it reaches the floor. Repeated dripping builds the deposit upward over a long period. A stalactite instead hangs downward from the roof, while coastal and glacial directions describe unrelated processes. Therefore, option C is correct.

Direct answer: C is correct. Gravity attracts atmospheric molecules towards Earth. The weight of the air above compresses the atmosphere most strongly near the surface, where air pressure and density are generally greatest. As altitude increases, there are fewer molecules above a given level, so pressure and density usually decrease. Gases remain mixed through much of the lower atmosphere, but gravity still controls the overall concentration and pressure pattern. A is wrong because gravity holds gases to Earth rather than sending all of them into space. B is wrong because density does not remain exactly constant with height. D is wrong because gravity acts on all atmospheric gases, not only ozone. Memory cue: “More air above means more pressure below.”