Fossil fuels such as coal, oil, amd natrual gas were formed over millions of years ago by

Fuels such as coal,oil,and natural gas were formed over millions of years from organic matter like plankton, plants, and other life forms

Your answer is d. silli hope this ! : ) i left an explanation down below if you need it: a sill forms when hot magma squeezes between layers of rock to form a hardened sheet of rock. a sill is basically a tabular sheet intrusion between old layers of sedimentary rock, volcanic beds, or in the direction of foliation inherent in metamorphic rock. the word sill means a concordant intrusive sheet.

Yeah, i guess that checks out because the unused brain is almost like a clean slate or a new car. it has more value than an older already used brain. -thomasnash