56–58  Over time, cacti literally reshaped themselves to fit their environment, by increasing their bulk and reducing the surface area they expose to the sun. Cacti stopped bearing leaves; they could no longer afford to supply broad-surfaced appendages with water. When the cacti dispensed with foliage, their stems and branches took over the leaves’ work of manufacturing food. By drawing energy from almost constant sunlight and moisture from their water-storing interior pulp, cacti can function all year round and flower even during lenghty droughts. Many other adaptations help cacti survive in a harsh environment. Their shallow, widespread root systems absorb maximum moisture in a region of brief rainstorms and thin quick-draining soil. The waxy finish on their tough skins retards moisture loss, and their armament of sharp spines affords protection from sun, wind and from the depredations of hungry, thirsty desert creatures.
56. What is the best title for this passage?
(A) The Habits of Flower Plants
(B) How the Cactus Became Extinct
(C) How Cacti Adjusted to Their Environment
(D) Using Cacti to Survive in the Desert