Final answer:
The simple sentence is Option A, which contains one independent clause with a subject and predicate, and expresses a complete thought without subordinate clauses.
Step-by-step explanation:
The question asks which sentence is a simple sentence. A simple sentence consists of a single main clause with a subject and a predicate and can stand alone as a complete thought. Therefore, the sentence that is a simple sentence is:
Option A: The baseball game seemed to drag on forever.
This sentence has one independent clause with a subject ('The baseball game') and a predicate ('seemed to drag on forever') and it expresses a complete thought without the presence of any subordinate clauses.