Sexual reproduction refers to the process that sperm and eggs of hermaphroditic germ cells combine to form fertilized eggs, and the fertilized eggs develop into new individuals. Asexual reproduction refers to the process that a new individual is directly produced by the mother without the combination of hermaphroditic germ cells. Vegetative propagation refers to the way in which vegetative organs (roots, leaves and stems) of plants produce new individuals.

A. Cutting, also known as cutting, is a common propagation method for cultivating plants. Some plants can be cut from stems, leaves, roots, buds and other parts. , or inserted into the soil, sand, or soaked in water, can be planted after taking root and become an independent new plant. Cutting is asexual reproduction, without the combination of bisexual germ cells, which does not meet the meaning of the question.

B. Grafting refers to grafting buds or branches of one plant to another plant, so that the combined two parts grow into a complete plant. It belongs to vegetative reproduction and does not meet the meaning of the question.

C, layering method: the method of burying the branches and vines of plants in a wet substrate, and cutting them from the mother plant after they take root to form a new plant.

D, the formation of seeds is through the combination of bisexual germ cells, so sowing belongs to sexual reproduction, which is in line with the meaning of the question.

So choose: D.