The correct answer is:
(d) all of the mentioned
Absorption dynamometers are used to measure the power output of an engine. The three types mentioned in your options are common types of absorption dynamometers:
1. Prony brake: A type of dynamometer that measures brake power by using friction to absorb engine output.
2. Rope brake: Similar to the prony brake but uses a rope wound around a drum to create resistance and measure power.
3. Hydraulic brake: Uses hydraulic fluid to absorb the power and measures the force required to drive the fluid through a controlled system.
Each of these methods is used to absorb engine power and determine its performance.