Which type of relationship can best be described as mutualism?

Mutualism is a type of symbiotic relationship where both species involved benefit from the interaction. The relationship between bees and flowering plants exemplifies this perfectly. Bees collect nectar and pollen from flowers, which they use for food. In the process, they facilitate the plant's reproduction by transferring pollen from one flower to another, allowing for fertilization and the production of seeds.

In contrast, the other options represent different types of ecological relationships that do not involve this reciprocal benefit. For example, remoras attach to sharks and gain food and transportation, but this does not significantly benefit the shark. Mistletoe can harm trees by drawing nutrients but can rarely be said to benefit them in return. Barnacles attach to whales, getting a free ride through nutrient-rich waters, yet this arrangement doesn't provide significant benefit to the whale. Thus, the interaction between bees and flowering plants is the clearest example of mutualism, as both parties derive essential benefits from their relationship.