As given in the paragraph rain seeps through rock and forms a vast aquifer.
An aquifer consists of permeable rocks or unconsolidated materials (sand, gravel, or slit ) that holds the water. This water can be extracted using a well.
Looking at the options bedroom and classroom are small as compared to the real-life aquifer so options a and b can be rejected.
option c must also be rejected as it is given rain forms vast aquifer. Vast here suggests the size of a lake.
