Explanation: Using two triodes in a push-pull Class A audio amplifier provides several significant advantages. Firstly, **increased power output** (A) is achieved because the two triodes combine their amplified signals, allowing for larger voltage and current swings across the load compared to a single-ended amplifier. Secondly, a major benefit is the **cancellation of even harmonic distortion** (B). Each triode amplifies opposite halves of the input signal. The non-linearities in each triode produce even harmonics, but because these harmonics are 180 degrees out of phase at the output transformer, they largely cancel each other out, resulting in cleaner audio reproduction. Thirdly, push-pull configurations prevent **DC saturation** of the output transformer core (C). The quiescent DC currents from the two triodes flow in opposite directions through the primary windings, cancelling their magnetic fields. This allows for smaller, more efficient transformers. Additionally, if a common cathode resistor is used, the opposing AC cathode currents from each triode tend to cancel, often **eliminating the need for a cathode bypass capacitor**, which can simplify biasing and improve transient response. Therefore, all the listed advantages are obtained, making "All of the above" the correct answer.