The Thick, Green Stems and Spike-Like Leaves of Cacti and Other

The thick, green stems and spike-like leaves of cacti and other drought-resistant bushes are adaptations to

A) take up atmospheric nitrogen in nutrient-poor environments.
B) increase gas exchange in oxygen-poor environments.
C) collect light in environments that have limited amounts of light.
D) conserve water in dry environments.
E) speed up heating and cooling in environments that have little temperature fluctuation.