✅ A simple sentence contains one independent clause , which means it has one subject and one predicate that expresses a complete thought. In option A, "The incredibly agile gymnast" is the single subject, and "flawlessly landed her final difficult dismount amidst thunderous applause" is its predicate.

The phrases "performing a routine of breathtaking flips and twists" (a participial phrase) and "amidst thunderous applause" (a prepositional phrase) act as modifiers and do not introduce additional independent or dependent clauses. Formula: Subject (S) + Verb (V) + (Modifiers) = One Independent Clause (IC).

❌ Option B is a complex sentence because it contains a dependent clause ("Although the incredibly agile gymnast performed her routine flawlessly") introduced by the subordinating conjunction "Although," followed by an independent clause.

❌ Option C is a compound sentence because it contains two independent clauses ("The incredibly agile gymnast performed a breathtaking routine" and "she flawlessly landed her final difficult dismount") joined by the coordinating conjunction "and."

❌ Option D is a complex sentence because it contains a relative clause ("who had trained for years"), which is a type of dependent clause, modifying "the gymnast."