7. early prospectors would extract shallow deposits of ore by\na. tunnel mining\nb. hydraulic mining\nc…

Brief Explanations:

Placer mining is often used for extracting shallow - lying deposits of valuable minerals. Tunnel mining is for deeper deposits, hydraulic mining uses high - pressure water for larger areas but not specifically for shallow deposits only, and quartz mining is not a general method for extracting shallow ore deposits.

Answer:

C. Placer mining