This question was posed to me in an international level competition.
This intriguing question originated from Flowering Plants Reproduction in division Sexual Reproduction in Flowering Plants of Biology – Class 12
To explain: Double fertilization is found in angiosperms only. In angiosperms, female gametophyte abruptly stops its growth at 8 nucleate stages. After the formation of the zygote and primary endosperm nucleus, further growth of embryo sac takes place.