C. The Senate and the House of Representatives are part of the legislative branch.
Explanation:
A compound subject is when there are two or more subjects in a sentence. "The Senate" and "the House of Representatives" are both nouns and they are the ones being discussed in the sentence, thus, they are the subject.
When there is a compound subject, the individual subjects are joined by a comma or by a coordinating conjunction like <em>or, nor, and </em>or <em>neither.</em>
The sentence the contains a compound subject is, option C. The Senate and the House of Representatives are part of the legislative branch. As you see, the subject of the sentence is more than one: The Senate and the House of Representatives. If there is more than one subject, it is called a compound subject.
