Covers the accounting equation

Correct answer: D. Cut-off of a meander neck

The correct answer is D. In a strongly curved meander, erosion on the outer banks and deposition on the inner banks can narrow the meander neck. During a flood, the river may cut through this narrow neck and adopt a straighter channel. Deposition then seals the abandoned ends, leaving the former bend as a detached, curved oxbow lake. The other choices describe unrelated agents.

Correct answer: C. Sparse vegetation and gully erosion by running water

Badland topography forms where soft, weakly consolidated material is exposed to intense runoff and has little protective vegetation. Rainwater concentrates into narrow channels, producing rapid rill and gully erosion. Closely spaced gullies create sharp ridges, ravines, and an intricately dissected landscape. Dense vegetation would reduce runoff erosion, while coral growth and subglacial deposits describe different environments. Therefore, option C correctly identifies the controlling conditions and process.

Correct answer: A. Widening of joints and cracks in limestone by solution

Karst drainage develops where soluble limestone contains joints, cracks and bedding planes. Carbonic-acid-rich rainwater enters these openings and dissolves the rock, gradually enlarging them into connected conduits. Water can then flow through the enlarged underground passages and form streams, caves and springs. Hence option A is correct. Delta retreat, coastal deposition and loess accumulation do not create underground limestone drainage.

Correct answer: A. Because one gas alone cannot perform all biological and thermal functions

Direct answer: A is correct. The atmosphere contains gases with different, complementary functions. Oxygen supports respiration for many organisms. Carbon dioxide is required by green plants for photosynthesis and also participates in the greenhouse effect. Nitrogen is an important raw material for biological compounds after it is converted into usable forms, and water vapour helps produce clouds and rainfall. No single gas can perform all these roles. B is not a scientific reason; atmospheric transparency depends on how radiation interacts with gases and particles. C is wrong because atmospheric mixing does not dry oceans. D is meaningless and false because gases are not living things and are not confined to fossils. A correctly explains why the mixture, rather than one gas alone, supports life and Earth’s environmental processes.

Correct answer: D. Because its amount depends on local temperature and nearby moisture sources

Direct answer: D is correct. Water vapour is a variable gas, unlike the relatively stable major gases whose proportions change much less across the lower atmosphere. Its amount depends strongly on local oceans, lakes, rivers, vegetation, soil moisture, evaporation and temperature. Warm air can hold more water vapour, while cooling causes condensation, cloud formation and possibly rainfall. These processes can remove vapour from one place and add it to another, so humidity and its effects vary greatly from region to region. A is wrong because water vapour continually moves through the water cycle. B is wrong because permanent gases are distributed widely, not only at the poles. C is wrong because most atmospheric water vapour comes from evaporation on Earth. D correctly explains its local variability.

Correct answer: A. It dilutes oxygen and keeps combustion intensity controlled

Answer: A. Combustion is a rapid oxidation process, and oxygen supports that process. Atmospheric air contains much more nitrogen than oxygen. Nitrogen is comparatively unreactive under ordinary conditions, so it acts mainly as a diluting component. Because oxygen is mixed with a large amount of nitrogen rather than present alone, fuels generally burn less fiercely than they would in nearly pure oxygen. B is wrong because nitrogen does not remove all oxygen; oxygen remains available for respiration and combustion. C is wrong because fire needs fuel as well as oxygen and heat. D is wrong because water vapour is not changed into a combustion gas by nitrogen. Memory cue: “Nitrogen is the air’s diluter, not an oxygen destroyer.”

Correct answer: A. It helps understand risks of cyclones, heavy rainfall, fog and air pollution

Atmospheric elements such as water vapour, pressure, wind, temperature and suspended particles are essential for monitoring weather hazards. Their patterns help forecasters identify cyclone development, intense rainfall, fog and pollution episodes, allowing warnings and preparedness measures. Option A is correct. Atmospheric study cannot stop tectonic plates or volcanoes, and it cannot guarantee a permanently stable sea level, so B, C and D are incorrect.

Correct answer: A. Stratosphere

Correct answer: A, the stratosphere. The main ozone layer lies in the stratosphere, above most weather activity. This region is generally dry and contains few ordinary clouds. However, over polar areas during exceptionally cold conditions, polar stratospheric clouds can form. Reactions on the surfaces of their ice or nitric-acid particles can change relatively inactive chlorine compounds into chemically active forms; sunlight can then help those forms participate in ozone destruction. B is wrong because the troposphere contains most ordinary clouds and weather, but it is not the characteristic location of polar stratospheric clouds. C is wrong because the exosphere is far too thin. D is not a standard atmospheric layer for this process. Memory cue: ozone and polar special clouds point to the stratosphere.