OPEC successfully raised the world price of oil in the 1970s and early 1980s, primarily due to A. an inelastic demand for oil and a reduction in the amount of oil supplied.
Inelastic demand is where the demand for a product does not increase or decrease with the fall or rise in its price. When someone believes that a product is inelastic to them, then their demand won't change even though the price changes. Since OPEC was able to raise the oil price and it was still consumed, it is a product of inelastic demand.