Concept:Structures labelled I (snail shell and cactus spines) protect the organism from harm.
Explanation:The shell of a snail is a hard outer covering.
It shields the snail from predators and physical injury.
The spines of a cactus are sharp, modified leaves.
They prevent herbivores from eating the cactus and reduce water loss.
Both structures act as physical barriers against danger.
Therefore, they are used for physical defence, not camouflage, chemical offence, or mimicry.
Answer:C. Physical defence
