Ex situ conservation is the conservation of selected rare plants or animals in places outside the natural forms.
Ex-situ conservation includes off-site collection and gene banks. Ex situ conservation is conserving the animals and plant outside the natural habitat.
Ex situ conservation includes offsite collection and gene banks.
Offsite collections are the live collection of file and domesticated species in the botanical garden.
Gene bank is an institution where available plant material is preserved in a viable condition. Seed Bank stores seed in the viable state.
So, the correct option is 'Seed bank'