Final answer:
The subclause in the sentence "He went to the window and looked out, but saw nobody." is option C. "but saw nobody", as it cannot stand alone as a complete sentence and is dependent on the main clause for context.
Step-by-step explanation:
The student has asked to identify the subclause in the sentence: "He went to the window and looked out, but saw nobody." To address this, it's important to note what constitutes a subclause (also known as a dependent clause). A subclause does not express a complete thought and cannot stand alone as a sentence; it is dependent on the main clause to provide complete meaning. In comparison, an independent clause can stand alone as a complete sentence.
In the sentence provided, "He went to the window and looked out" are actions related to the same subject, making them a part of the main clause rather than a subclause. The correct option for the subclause is C. "but saw nobody", as 'but' serves as a coordinating conjunction, which introduces the subclause that cannot stand alone and provides additional information to the sentence.