Which resource of the ocean floor is not currently being used, but in the future could become an important energy source?

Deep sea creatures and mineral wealth can become a potential energy source.

Explanation:

Deep-sea organisms community that lives deep down near the ocean floor have not been fully explored and thus their holds a potential energy source for the future generations. To extract these deep ocean creatures and make use of their special abilities that can be used as an energy source.  The use of deep mining projects can extract many unknown hidden resources that are potential for the future. The corals that live on the ocean floor are also a potential resource for man in the future.

Nimbostratus is the correct answer.
explanation: nimbostratus clouds are the type of clouds that are mostly likely present on gray, rainy day. these clouds produce continuous rain, snow and there is no thundering or lightening either.