Answer: D). The students all used methods of asexual reproduction to produce new plants.
Asexual reproduction is a mode of reproduction which occurs in simple organisms, in this a single parent produces numerous offsprings. This reproduction method does not requires gamete formation. Stems of raspberries, roots of potatoes, stems of rose plants and bulbs of onion all these plant parts can be used to generate new plants by the process of vegetative propagation which is a asexual mode of reproduction.