Answer:
D. OPEC actions
Step-by-step explanation:
The downfall of the US oil industry in the 1980s was caused by a reduced demand for oil caused by the energy crises of the 70s and with this reduced demand, there became an oil glut, because the production was also increased.
Therefore, this downfall of the oil industry in America in the 1980s was caused by increase in oil prices by OPEC (Organisation of Petroleum Exporting Countries).