Read the following passage about prebiotics and then answer the question that follows: Prebiotics are the lesser-known gut-health promoters which serve as food for good bacteria inside the gut. "We found that dietary prebiotics can improve non-REM (random eye movement) sleep, as well as REM sleep after a stressful event," said Robert Thompson, a PhD researcher at University of Colorado Boulder in the U.S. Prebiotics are dietary fibres found naturally in foods like artichokes, raw garlic, leeks and onions. When beneficial bacteria digest prebiotic fibre, they not only multiply, improving overall gut health, but they also release metabolic by-products. Researchers fed three-week-old male rats a diet of either standard chow or chow that included prebiotics. They then monitored the rats body temperature, gut bacteria and sleep-wake cycles using electroencephalogram (EEG), or brain activity testing over time. Findings revealed that the rats on the prebiotic diet spent more time in non-rapid-eye-movement (NREM) sleep, which is restful and restorative, than those on the non-prebiotic diet. What are prebiotics?

Introduction / Context:
This reading comprehension question assesses careful reading of a scientific-style passage about prebiotics and their effects on sleep. The key skill is to identify exactly how the passage defines the term “prebiotics” rather than rely on vague prior knowledge. The passage explains what prebiotics are, where they are found, and how they influence gut bacteria and sleep patterns in experimental rats.

Given Data / Assumptions:
- Prebiotics are described in the passage as “gut-health promoters which serve as food for good bacteria inside the gut”. - Later, the passage states that prebiotics “are dietary fibres found naturally in foods like artichokes, raw garlic, leeks and onions”. - The question asks directly: “What are prebiotics?” - The options include dietary fibres, bacteria, specific foods, and related concepts.

Concept / Approach:
In reading comprehension, many questions test recognition of definition sentences. When a passage contains expressions like “Prebiotics are ...” followed by a clear description, that sentence usually holds the precise answer. The candidate should locate and quote the definition rather than interpret the word according to external knowledge. Here, the crucial line is “Prebiotics are dietary fibres found naturally in foods like artichokes, raw garlic, leeks and onions.” This line tells us the category to which prebiotics belong.

Step-by-Step Solution:
Step 1: Scan the passage for sentences that begin with the word “Prebiotics” and a linking verb like “are”. Step 2: Identify the sentence: “Prebiotics are dietary fibres found naturally in foods like artichokes, raw garlic, leeks and onions.” Step 3: Note that in this sentence, “dietary fibres” is the general noun that defines what prebiotics are. The list of foods is only an example of where these fibres occur. Step 4: Compare this with option A, which says “Dietary fibres”. This exactly matches the key phrase in the definition. Step 5: Evaluate other options. Option B, “Bacteria”, describes the good organisms that consume prebiotics, not the prebiotics themselves. Option C, “Foods like artichokes”, lists food sources, not the substance. Option D, “Gut microbiota”, refers to the community of microorganisms in the gut. Option E, “Digestive enzymes”, are chemicals that break down food and are not mentioned as prebiotics. Step 6: Conclude that the precise answer is option A.

Verification / Alternative check:
A different way to verify is to rephrase the relevant line: “Prebiotics are dietary fibres that act as food for beneficial bacteria.” None of the other options can be substituted into this sentence without changing its meaning. For instance, “Prebiotics are bacteria” would confuse the bacteria with their food. Similarly, “Prebiotics are artichokes” clearly fails, because artichokes are only an example of a food containing such fibres. This confirms that only “dietary fibres” fits all parts of the passage.

Why Other Options Are Wrong:
Bacteria: The passage states that prebiotics serve as food for beneficial bacteria; they are not themselves bacteria. Foods like artichokes: These are sources of prebiotic fibres and are not identical to prebiotics as a category. Gut microbiota: This term refers to the community of microorganisms in the digestive tract, which benefit from prebiotics. Digestive enzymes: These are substances that assist in breaking down food, but the passage does not equate them with prebiotics.

Common Pitfalls:
Students sometimes rush through the passage and confuse “food for bacteria” with “bacteria” themselves. They may also pick examples, such as artichokes, instead of the general class. In scientific passages, it is important to distinguish between the substance being defined, its sources, and the organisms that use it. Careful reading and attention to definition sentences help avoid these errors.

Final Answer:
According to the passage, prebiotics are dietary fibres.