Silk is not a plant product. It is the secretion of silk gland of larva of an insect Bombyx mori. Silk is a natural fibre that is obtained from the cocoons of silkworms. There are stages of obtaining silk that include rearing silkworms, cocoon harvesting and silk production. The quality of the silk produced depends on the quality of the mulberry leaves on which the worms had fed, the conditions of rearing of the silkworms and the handling of the cocoon harvesting.
So, the correct answer is (D): silk
Sexual reproduction in flowering plants takes place or happens when the production of a new organism occurs from two parents by making use of their gametes or sex cells. Both sexual and asexual reproduction can be found in plants. Nearly all flowering plants reproduce sexually. Flowers play a captious role in the process as it carries both the male and female reproductive parts commonly known as androecium and gynoecium respectively.