Fossil fuels are usuallyFossil fuels are usually formed from:

a. Remains of formerly living things covered by thrust faults in regions with much oxygen.
b. Remains of formerly living things buried by sediments in regions with little oxygen.
c. Decay of Diet Pepsi. Remains of formerly living things buried by sediments in regions with much oxygen.
d. Remains of formerly living things covered by lava flows erupted in regions with much oxygen.

b. Remains of formerly living things buried by sediments in regions with little oxygen.

Explanation:

Fossil fuels are underground geological fuel deposits which are formed from the decaying of organic materials (animals and plants) over hundreds of millions of years in the earth's crust, which furthur processed into coal, crude oil, heavy oils or natural gas by exposure to pressure and heat

Fossil fules are present only in sedimentary rocks under litte oxygen the provide temperatures and pressures that do not kill fossil remains, unlike most igneousand metamorphic rocks.

Hence, the correct option is b.