Answer:
A. By storing a great variety of seeds in case one variety goes extinct in the wild.
Step-by-step explanation:
We know that in nature, there are many types of species that dominate others to grow well, live well, etc. It is also true for plants. If there are many types of plants cultivated together, it is natural that there will be some dominating plant species that will dominate the others to grow well. Now, if any plant can't grow well, it won't be able to reproduce its next generation. As a result, it might happen that, in one day, it will become extinct in the wild. Gene bank is used to save genes so that, they remain in the world and can be used if needed. The seed bank is also used for the same purpose. So, it will be helpful for the human to storing out a great variety of seeds in case one variety goes extinct in the wild.