Deserts such as the Sahara are generally found between 20° and 30° latitudes in the western parts of the continents. This is because these regions

Answer: (a) Have off-shore winds throughout the year

Trade winds blow from land to sea on west coasts at 20–30°, so they bring no moisture.

The idea

A desert forms where water supply from rain is persistently low relative to water loss. Subtropical sinking air discourages clouds, and offshore winds supply little sea moisture to many western margins. Cold currents can further stabilise the coastal air. High temperature alone cannot account for this pattern.

Subtropical high brings descending air → Compression lowers relative humidity → Offshore flow carries air away from the coast → Cold coastal water limits deep convection → Rain remains scanty → Arid conditions develop

Why the others are wrong

(b) Currents there are cold, not warm.

(c) The doldrums are at the equator.

(d) Heat alone doesn’t make a desert.

Elimination technique

The doldrums are an equatorial rising-air belt, not the 20–30° dry belt. Warm currents do not supply the usual coastal-desert mechanism, and heat alone cannot explain the location. Offshore flow is the relevant process among the choices.

Also know

Sahara is a broad subtropical desert, not just a narrow coastal strip. Namib is linked to Benguela and Atacama to Humboldt; both can have fog despite little rain. Kalahari lies farther inland, while Gobi is a cold interior desert. Doldrums near the equator have rising moist air rather than the usual hot-desert circulation.