Explanation: For an NPN transistor to operate as a Class A amplifier, it must be biased in its **active region**. In the active region: * The **base-emitter (BE) junction** must be **forward biased**. This allows a small base current to flow, which controls a much larger collector current. Think of it as opening a gate for current from the emitter to the collector. * The **collector-base (CB) junction** must be **reverse biased**. This condition allows the collector to draw electrons from the base, establishing the amplified current flow and providing the necessary voltage drop for amplification. Therefore, option D correctly describes the biasing conditions for an NPN transistor operating in Class A: the base-emitter junction is forward biased, and the collector-base junction is reverse biased. Options A and B describe saturation and cutoff, respectively, neither of which allows for linear amplification over the entire input cycle. Option C describes an incorrect or unusual biasing state.