The correct answer is pollen. Pollen is the plant's male reproductive cells, which contain the sperm. In order for a flower to reproduce, the pollen needs to move from the stamen to the pistil. The stamen is the male part of the flower and produces the pollen, while the pistil is the female part of the flower that contains the ovules. The transfer of pollen to the pistil can occur through various mechanisms, such as wind, water, or pollinators like bees, butterflies, or birds. Once the pollen reaches the pistil, it fertilizes the ovules, leading to the formation of seeds. So, for a flower to reproduce, pollen must move from the stamen to the pistil.
