Concept:Xerophytic plants live in dry habitats where water is scarce.
Explanation:The primary difficulty for these plants is the shortage of water in their environment.
To cope, they develop thick cuticles, sunken stomata, and deep root systems.
These adaptations help reduce water loss and improve water absorption.
So, the key issue is not competition for sunlight, excess water, or weak roots.
It is the lack of enough water.
Answer:D. Lack of adequate water