The correct option is C Ovule
Stems, leaves and buds can be used as vegetative propagules in different plants. For example, runners seen in lawn grass is an example of vegetative propagation by stems. Adventitious buds are seen in Bryophyllum which is an example of vegetative propagation by leaves. Lastly, the bulb is a type of underground stem which is seen in onions.
Ovule, however, is a structure seen in sexually reproducing plants. The ovule consists of cells that undergo meiosis to produce the embryo sac. This embryo sac consists of female gametes. In the case of flowering plants, the fusion of male and female gamete occurs inside the ovule. Thus ovule is a structure associated with sexual reproduction and cannot be used as a vegetative propagule.