Blank (i): A. indefinitely
- Why? The first part of the sentence establishes a condition: "If there is nothing to absorb the energy." In physics, if an object or wave (like sound) is in motion and encounters no resistance or absorption, it will continue its path without stopping.
- B. erratically suggests a random, unstable path, which doesn't fit the logic of a lack of absorption.
- C. slowly is incorrect because absorption affects the energy and duration of the wave, not necessarily its constant speed through a specific medium.

Blank (ii): E. diminishes
- Why? This is the "Adaptive Trap" mentioned in your earlier context-a subtle logic check. Even if a sound wave isn't being absorbed by an object, its intensity (loudness) naturally drops as it spreads out over a larger area. This is known as the Inverse Square Law. As the wave moves further from the source, the same amount of energy is spread over a larger "sphere," making the sound quieter.
- D. alleviates usually refers to lessening pain or a problem, which is the wrong context for physical intensity.
- F. mitigates means to make something less severe or harmful; again, this is a "human" or "social" verb rather than a mechanical description of wave physics.

Final Completed Sentence
If there is nothing to absorb the energy of sound waves, they travel on (i) indefinitely, but their intensity (ii) diminishes as they travel further from their source.