The best definition of a flower from the options provided is: the female reproductive structures that develop into seeds in a seed-bearing plant.
However, it is important to note that a flower generally consists of both male (stamens, which produce pollen) and female (pistils, which contain the ovary) reproductive structures. Therefore, a more comprehensive definition of a flower encompasses both its male and female functions. The best overall understanding of a flower would include its role in reproduction for seed-bearing plants.