Question

which organisms were the source of oil and gas? dinosaurs giant insects microscopic marine plankton early mammals

Explanation:

Oil and gas are formed from the remains of microscopic marine plankton. Over millions of years, these organisms were buried under sediment and subjected to heat and pressure, which transformed them into hydrocarbons. Dinosaurs, giant insects, and early mammals are not the primary sources of oil and gas.

Answer:

Microscopic marine plankton