Final answer:
In seedless plants, a fertilized egg develops into b) a sporophyte, the diploid phase of the plant's lifecycle, which will eventually produce spores to continue the cycle of reproduction.
Step-by-step explanation:
In seedless plants, a fertilized egg, also known as a zygote, develops into an embryo and then into a new plant known as a sporophyte. This process signifies the alternation of generations in plant life cycles, where the sporophyte is the diploid, or a double set of chromosomes, a phase that follows the gametophyte, or haploid phase. The sporophyte generation is prominent in the life cycles of seed plants, whereas the gametophyte is much reduced and is often not easily observed without microscopic examination. The gametophyte generation is responsible for producing gametes, while the sporophyte generation produces spores through meiosis that can develop into gametophytes. Therefore, when considering the development process in seedless plants, the correct answer to the question is "B) a sporophyte." After fertilization, the zygote grows into an embryo within the protective tissues of the gametophyte, eventually becoming a mature sporophyte that will produce spores to continue the cycle of reproduction.