In Desert Environments, Many Larger Plants Serve as "Nurse" Plants

Multiple Choice

In desert environments, many larger plants serve as "nurse" plants for smaller species that grow beneath them and benefit from their shade. Which characteristic of this association suggests that coevolution is not a major factor?

A) The association is facultative, rather than obligate.
B) The association involves commensalism, rather than mutualism.
C) A single nurse species can protect many different smaller species.
D) The association occurs only in the desert.