Flowering plants need to get pollen from one flower to another, either within a plant for self-pollination or between plants of the same species for cross-pollination to occur. However, pollen can't move on its own, so animals or the wind (and water in rare cases) move the pollen for plants.
To, sustain animal visits, the flowers have to provide rewards to the animals. Nectar and pollen grains are important floral rewards to the animal pollinators such as moths, butterflies, wasps, bees, birds, etc.
So, the correct ans is "Nectar and pollen grains".