(d): The abnormal baby has an extra $X$ chromosome, thus it must have been produced by fusion of abnormal $XX$ ovum with a normal $X$ sperm. Abnormal $XX$ sperm is not possible because, males have $XY$ genotype, and if produce abnormal sperms, then $XY$ sperms and $O$ sperms will be produced. If fusion of multiple gametes have occurred (either two ova with one sperm or two sperms with one ovum), then the human baby will have triploid genotype not the trisomy of sex chromosomes.