Which of the following best describes a complex sentence?

A complex sentence is defined as a sentence that contains one independent clause and at least one dependent clause. The presence of the dependent clause adds complexity to the structure, as it cannot stand alone and relies on the independent clause to provide complete meaning. For example, in the sentence "Although it was raining, we went for a walk," "Although it was raining" is the dependent clause, while "we went for a walk" serves as the independent clause.

In contrast, a sentence with two independent clauses describes a compound sentence. A simple sentence consists of a single independent clause with no dependent clauses, making it straightforward and uncomplicated. A compound-complex sentence, on the other hand, combines elements of both compound and complex sentences, containing at least two independent clauses and at least one dependent clause, which further deviates from the definition of a complex sentence itself. Therefore, the choice that accurately captures the essence of a complex sentence is the one that includes both an independent and a dependent clause.