Answer:
The Cactus wren and Cholla cactus have a commensalism relationship in which the only one with benefits is the cactus wren and neither of them has a disadvantage.
Step-by-step explanation:
First of all, this relationship is very special. The cactus wren nests in the chollas. While the chollas don't harm them for doing so, in contrast, they provided protection for their eggs from predators. The Chollas don't receive any benefit and also no harm. Therefore, the only one that benefits here is the Cactus Wren. However, they don't damage or threaten the Chollas' lives.