✅ The correct answer is A. This is a direct application of deductive reasoning, specifically a form of Modus Ponens or a categorical syllogism.

The first premise establishes a general rule: if someone is a professional athlete, then they train rigorously. The second premise identifies Sarah as a professional athlete.

Therefore, it necessarily follows that Sarah fits the criteria for rigorous training based on the established rule.

❌ Option B is incorrect. The statements assert that all professional athletes train rigorously, but they do not claim that only professional athletes engage in rigorous training; others might also train rigorously.

❌ Option C cannot be deduced from the given statements. The premises provide no information about individuals who train rigorously but are not professional athletes, so this conclusion is not necessarily true based *solely* on the given information.

❌ Option D is incorrect. It reverses the relationship stated in the first premise; "All A are B" does not logically imply "All B are A." Just because all professional athletes train rigorously does not mean everyone who trains rigorously is a professional athlete.

✅ A sound deductive argument is defined by two conditions: it must be valid, and all of its premises must be true.

If an argument is valid, the conclusion *must* logically follow from the premises, meaning if the premises are true, the conclusion cannot be false.

Therefore, if a deductive argument is also sound (has all true premises), its conclusion is guaranteed to be true.

❌ Option A describes an ampliative argument, which is characteristic of inductive reasoning, where conclusions often expand upon the information in the premises.

❌ Option B is incorrect because the conclusion of a deductive argument is only guaranteed if the premises are true; if premises are false, the conclusion might still be false, even in a valid argument.

❌ Option D describes inductive reasoning, which typically moves from specific instances to broader, probable generalizations, not guaranteed conclusions.

✅ Option D is the only conclusion that can be logically and certainly deduced from the given premises.

✅ Deductive logic ensures that if the premises are true, the conclusion must also be true, moving from a general rule ("All healthy plants require sunlight") to a specific instance ("My indoor fern is a healthy plant").

❌ Option A introduces uncertainty ("might") and suggests an alternative light source, which is not directly deducible from the given information.

❌ Option B is a true statement, but it is not the specific deductive conclusion derived by combining both premises; it's more of an observation or a partial truth from the second premise.

❌ Option C is an illicit conversion of the first premise; just because all healthy plants need sunlight doesn't mean everything that needs sunlight is a healthy plant.

✅ Option B correctly defines a valid deductive argument: its structure ensures that if the premises are assumed true, the conclusion logically follows with absolute certainty.

❌ Option A is incorrect because a deductive argument can be valid even if its conclusion is factually false, provided that at least one of its premises is also false.

❌ Option C describes a *sound* argument, which is a valid argument with all true premises; however, validity itself only concerns the logical structure, not the factual truth of the premises.

❌ Option D describes inductive reasoning, where conclusions often introduce new information and are probable rather than certain; deductive conclusions are contained within the premises.

✅ A valid deductive argument is defined by its structure: if all its premises are assumed to be true, then its conclusion *must* necessarily be true. The truth of the premises guarantees the truth of the conclusion.

❌ Option B describes inductive reasoning, which aims for probability rather than certainty in its conclusions.

❌ Option C describes a *sound* deductive argument, which is a valid argument with the additional condition that all its premises are actually true; validity alone does not require premises to be factually true, only that the conclusion logically follows *if* they were true.

❌ Option D is characteristic of inductive reasoning (or abduction), where the conclusion expands upon the information in the premises; deductive conclusions are non-ampliative, meaning they only make explicit what is already implicitly contained within the premises.