The correct answer is a) double fertilization.
Double fertilization is a process that only occurs in flowering plants (angiosperms). During this process, one sperm cell fertilizes the egg cell to form the zygote, while another sperm cell fuses with two polar nuclei to form the triploid endosperm. This endosperm serves as nutritive tissue for the developing embryo, making double fertilization a unique characteristic of flowering plants. The other options, such as having an embryo surrounded by nutritive tissue, haploid gametophytes, or pollen production, are not exclusive to flowering plants and can also be found in other plant groups.