Choose the cells of embryo sac whose ploidy is changed after double fertilization.
A. Synergids              B. Egg cell                C. Central cell                       D. Antipodals.

Egg cell is haploid prior to fertilization and after fertilization it becomes diploid zygote. Central cell is dikaryotic and haploid prior to ferilisation but after fertilization it becomes uninucleate triploid Primary endosperm cell with primary endosperm nucleus. Synergids and antipodals are not fertilized.