Select the single-word substitute that best expresses the meaning of the phrase: "Average in amount, intensity, quality, or degree."

Introduction / Context:
Single-word substitution questions test whether you can condense a descriptive phrase into a precise English word. The given phrase describes something that is neither very high nor very low in amount, intensity, quality or degree. In everyday language, we often use one common adjective to describe such a middle or average level. Your task is to identify that word among several distractors that have entirely different meanings.

Given Data / Assumptions:

• Phrase: "Average in amount, intensity, quality, or degree."
• Options: moderate, supernatant, hobble, hum and one extra distractor.
• We assume that the question is asking for the most common and widely accepted English word that matches this definition.
• The context can be anything: weather, political opinions, speed, price, and so on.

Concept / Approach:
The adjective "moderate" is widely used to describe something that is of average or reasonable level. For example, we talk about "moderate rainfall", "moderate exercise" or "moderate views". In all these cases, the idea is that the thing is neither extreme nor negligible. The other options have unrelated meanings: "supernatant" refers to the clear liquid floating above a sediment in a scientific context; "hobble" is a verb meaning to walk awkwardly or to hinder; "hum" is a low continuous sound; and "middling", while also sometimes meaning average, is less commonly used and often informal. The best match for the given definition in standard usage is "moderate".

Step-by-Step Solution:
Step 1: Convert the phrase into a simpler synonym in your own mind. "Average in amount or intensity" suggests "not extreme", "reasonable" or "moderate".Step 2: Examine option A, "moderate". Dictionaries define moderate as "average in amount, intensity, quality, or degree", which matches the phrase almost word for word.Step 3: Examine option B, "supernatant". This is a technical word used mainly in chemistry and biology to describe a liquid floating above a solid residue; it has nothing to do with average or intensity.Step 4: Examine option C, "hobble". This verb means to limp or to restrict someone's movement or progress; again, unrelated to the idea of average level.Step 5: Examine option D, "hum". It usually refers to a low continuous sound or a buzz; it does not indicate a degree or amount.Step 6: Even though "middling" can sometimes mean "average", "moderate" is the textbook definition that directly matches the given phrase. Therefore, select "moderate".

Verification / Alternative check:
Compare sample usages: "moderate exercise" means exercise of average intensity, "moderate income" means average or reasonable income. Replace "moderate" with the phrase from the question and the meaning stays the same: "exercise that is average in intensity", "income that is average in amount". Trying to replace with "supernatant", "hobble" or "hum" produces nonsense sentences. This confirms that "moderate" is the correct single-word substitute that aligns exactly with the given description.

Why Other Options Are Wrong:

• Supernatant: Technical scientific term for a liquid layer; does not describe degree or intensity.
• Hobble: Means to limp or to restrict; unrelated to level or amount.
• Hum: A low, continuous sound; not connected to the concept of average intensity.
• Middling: While sometimes meaning average, it is less precise and more informal. "Moderate" is the textbook equivalent used in definitions.

Common Pitfalls:
Some students may be tempted by unusual words, assuming that the "hardest looking" word must be correct. Others might overthink the question and look for rare vocabulary when a very common word like "moderate" is the best answer. To avoid these traps, always match the definition exactly and think of simple synonyms first. If a common word matches perfectly, there is no need to search for something exotic. Practising single-word substitution with dictionary definitions helps solidify these connections in your memory.

Final Answer:
The best single-word substitute for the phrase is moderate.