B
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
In a desert environment, cactus wrens often build their nests in cholla cacti to avoid predators. This behavior does not hurt the cacti. Which type of relationship do cactus wrens and cholla cacti demonstrate?

### Choices:
A. competitive
B. commensalism
C. mutualism
D. parasitism

### Answer:
