Correct Answer - A
An ideal engine called a Carnot engine serves as ideal heat engine. This ideal engine turns put to be the best at using energy as heat to do useful work. Carnot engine comprises four cycles. During each cycle of engine , the working substance absorbs energy `|Q_(H)|`as heat from a thermal reservoir at constant temperature `T_(H)` and discharges energy `|Q_(L)|` as heat to a secon thermal reservoir at a constant lower temperature `T_(L)` . Thus, carnot cycle provides a way of determine the maximum possible efficiency achievable with reservoures of given temperature.
Hence option (a) is true.