Which of the following illustrates a parasitic relationship?

A parasitic relationship occurs when one organism benefits at the expense of another organism, often harming it in the process. In the case of a lamprey sucking on a fish, the lamprey attaches itself to the fish and feeds on its blood and bodily fluids. This interaction clearly demonstrates parasitism because the lamprey derives nourishment and benefits by harming the fish, which may experience negative health consequences or even death due to the loss of blood and damage to its body.

The other options depict different types of relationships in nature. For example, the bee pollinating a flower represents mutualism, where both organisms benefit; the bee collects nectar for food while helping the flower with reproduction. The bird nesting in a tree portrays commensalism, as the bird gains habitat and protection, but the tree is neither helped nor harmed. Finally, a cow grazing on grass is typically seen as a form of herbivory; the cow benefits by consuming food, while the grass is harmed but can regrow. Thus, option B most accurately illustrates a parasitic relationship.