A thick, black liquid formed from the buried remains of microscopic marine organism is oil.
Answer: B) Oil
Explanation
The dead bodies of microscopic marine organisms such as plants, plankton, fish, octopus etc. remains in the bottom of the marine bodies for several decades.
Even the bodies of human beings are present in the bottom of the marine bodies if the death is caused by natural disasters like flooding or extinction of whole region under water.
So these dead bodies get decayed in the bottom of the marine bodies for several years and after complete decaying they will release a liquid which will have high viscosity or thickness and black in color.
These liquid is termed as fossilized oils which can be refined as petroleum oil, gasoline and it can also be converted as natural gas if the decaying time extends over a long time.