Final answer:
A transistor must be biased in the active region to properly amplify AC signals, ensuring a small input can translate into a larger output in a linear manner, although high gain and low input impedance are also beneficial.
Step-by-step explanation:
In order for a transistor to properly amplify AC signals, it must be biased in the active region. When a transistor operates in this region, its base-emitter junction is forward biased, which ensures that a small input signal can be translated effectively into a larger output signal. If the transistor is not biased correctly, it may operate in the cutoff region (where it acts as an open circuit) or the saturation region (where it acts as a closed circuit), both of which are undesirable for amplification purposes.
Gaining a high level of amplification requires sufficient gain, but the positioning in the active region is also crucial as it allows the transistor to respond linearly to the input signal. Although a low input impedance can be beneficial for signal coupling, and having a transistor connected in parallel with the load can affect power delivery, the biasing condition is fundamentally important for the proper operation of the transistor as an amplifier.