The correct option is C Gene banks
Gene banks are a type of biorepository, which preserve genetic material. For plants, this could be by freezing cuttings from the plant, or stocking the seeds (e.g., in a seed bank). For animals, this is the freezing of sperm and eggs in zoological freezers until further need. With corals, fragments are taken which are stored in water tanks under controlled conditions.
Plant genetic material in a 'gene bank' is preserved at −1960C in liquid nitrogen as mature seed (dry).