The correct answer is mutualism. Mutualism is a type of symbiotic relationship where both organisms involved benefit from the interaction. In the case of a bee eating a flower's nectar and picking up the flower's pollen, the bee gets a source of food (nectar) while also unintentionally transferring pollen from the stamen (male part of the flower) to the pistil (female part of the flower), which aids in pollination and ensures the flowers can reproduce.
