The correct answer is option 3: stigma. The stigma is the part of the flower that receives pollen grains during pollination. It is located at the top of the pistil, the female reproductive organ of the flower. The stigma is typically sticky or has small hairs to help trap and hold onto pollen grains. Once the pollen grains land on the stigma, they can then germinate and grow down through the style, another part of the pistil, to reach the ovary where the ovules are located. The ovary contains the female gametes, or eggs, which can be fertilized by the pollen grains to initiate the process of reproduction in flowering plants. Therefore, the stigma plays a crucial role in the successful pollination and fertilization of a flower.