Which of the following sentences is an example of a complex sentence?

A complex sentence is defined as one that contains an independent clause and at least one dependent (or subordinate) clause. In the provided example, "Because I was tired, I went to bed early," there is a dependent clause ("Because I was tired") that cannot stand alone as a complete sentence because it introduces a condition or reason. This clause is connected to the independent clause "I went to bed early," which can stand alone as a complete thought. The combination of these clauses is what characterizes the sentence as complex.

In contrast, other options are simple or compound sentences. For instance, the first option contains two independent clauses joined by a conjunction, making it compound rather than complex. Similarly, the third option consists of two independent clauses and is therefore also compound. The fourth sentence presents a single independent clause, making it a simple sentence. Recognizing the structure of clauses within a sentence is essential for identifying complex sentences accurately.