Which of the following is an example of a subordinating conjunction?

A subordinating conjunction is a word that connects an independent clause with a dependent clause, introducing a subordinate idea. In this context, "because" serves this function effectively. It indicates a reason or cause and introduces a clause that cannot stand alone as a complete sentence, such as "Because it was raining." This structure highlights how one thought relies on the other for full meaning, making "because" a perfect illustration of a subordinating conjunction.

In contrast, the other options—"and," "but," and "nor"—are coordinating conjunctions. They are used to connect words, phrases, or independent clauses that are similar or can stand alone independently. For instance, "and" connects two ideas of equal importance without establishing a dependent relationship, making it unsuitable for this particular question focused on subordinating conjunctions.