18.a) Humidity is the amount of water vapor present in the atmosphere.

18.a) Humidity is the amount of water vapor present in the atmosphere.

18.b) The unit of measurement for absolute humidity is grams per cubic meter ($\text{g/m}^3$).

18.c)

• Absolute humidity is the actual mass of water vapor present in a given volume of air.
• Relative humidity is the ratio of the actual amount of water vapor in the air to the maximum amount of water vapor the air can hold at a specific temperature, expressed as a percentage.

18.d) Three factors that influence humidity are:

• Temperature: Warmer air can hold more moisture, so higher temperatures generally lead to higher humidity if moisture is available.
• Proximity to water bodies: Areas near oceans, lakes, or large rivers tend to have higher humidity due to continuous evaporation.
• Vegetation: Transpiration from plants releases water vapor into the atmosphere, increasing humidity, especially in densely vegetated areas.

18.e) Three uses of moisture in the atmosphere are:

• Precipitation: Atmospheric moisture condenses to form clouds and eventually falls as rain, snow, or other forms of precipitation, which is vital for water supply and ecosystems.
• Regulation of temperature: Water vapor is a greenhouse gas, absorbing and re-emitting infrared radiation, which helps to regulate Earth's temperature and prevent extreme temperature fluctuations.
• Cloud formation: Moisture is essential for the formation of clouds, which reflect solar radiation, influencing Earth's energy balance and climate.

19.a) The highlands marked are:

• A: Atlas Mountains
• B: Ahaggar Mountains
• D: Ethiopian Highlands
• E: Drakensberg Mountains

19.b) The highlands marked A, the Atlas Mountains, were formed by the collision of the African and Eurasian tectonic plates. This collision caused the Earth's crust to fold and uplift, creating a series of parallel mountain ranges.

19.c) A cash crop most grown in the highland E (Drakensberg Mountains) and its surrounding regions is sugar cane.

19.d) (i)

• Fault steps: A series of parallel faults that create a stepped appearance on the landscape, where each step represents a block of land that has been uplifted or down-dropped relative to its neighbors.
• Escarpment: A long, steep slope or cliff that separates two relatively level areas of different elevations, often formed by faulting or erosion.

19.d) (ii) Two examples of landforms resulting from faulting are:

• Rift valleys
• Block mountains (Horsts)

20.a) The climate characteristics of this weather station are:

• Temperature: The station experiences consistently high temperatures throughout the year, ranging from $28^\circ\text{C}$ to $31^\circ\text{C}$, indicating a hot climate.
• Rainfall: It receives a high amount of annual rainfall, with distinct wet seasons (e.g., Jan-Apr and Sep-Oct) and relatively drier periods (e.g., Jun-Aug), characteristic of a monsoonal or tropical climate.

20.b)