Answer: "Small submarines that can be launched from ships" is the complete subject of the sentence.
Explanation: The complete subject of a sentence includes the simple subject, or the head word of the subject, as well as its modifiers. Therefore, the complete subject is the part of the sentence that indicates what or who is going through a process, performing an action or experiencing an emotion. In the sentence provided ("Small submarines that can be launched from ships allow explorers to get close to shipwrecks and marine life")<u>, "small submarines that can be launched" is the complete subject since it includes the simple subject ("submarines") and its modifiers</u> (the adjective "small" and the relative clause "that can be launched". Moreover, <u>the main verb ("allow") makes reference to a feature of this subject. </u>
