Which statement has the correct causal relation between factor and vegetation?

Correct answer: Low rainfall can favour thorny vegetation

The direct answer is A: low rainfall can favour thorny vegetation. Vegetation depends on factors such as rainfall, temperature, soil, and relief. Thorny bushes and scrub often occur in dry regions because they are adapted to limited water. Step by step: low rainfall means water is scarce; plants must reduce water loss; many thorny plants have small leaves, spines, waxy surfaces, or deep roots; these adaptations help them survive; therefore low rainfall can favour thorny vegetation. Option A is correct and uses the careful word 'can', because other conditions also matter. Option B is wrong because sandy soil does not always produce evergreen forests; evergreen forests generally need suitable warmth and abundant moisture. Option C is wrong because temperature usually decreases with increasing altitude, though local conditions may vary. Option D is wrong because deforestation removes forest cover rather than increasing it. Memory cue: dry climate, water-saving plants, thorns.