Where would a submarine most likely be used as an exploration tool? 

A)  in the lithosphere 
B)  in the hydrosphere 
C)  in the biosphere 
D)  in the atmosphere

Submarine

A watercraft capable of independent operation underwater, often used for naval or research purposes.

Hydrosphere

All the waters on the earth's surface, such as lakes and seas, and sometimes including water over the earth's surface, such as clouds.

Exploration Tool

Equipment or software used in the discovery and investigation of new geographical areas or resources.