Final answer:
Presenting common knowledge, like the law of gravity, without citing a source is not considered plagiarism because these are widely known facts that an educated adult is expected to know and can be easily verified.
Step-by-step explanation:
Plagiarism is the act of using someone else's words or ideas without proper attribution. When considering which of the provided options is not an example of plagiarism, we must identify the choice that aligns with acceptable academic practices. Presenting someone else's words or ideas as your own, or paraphrasing without citation, are clear examples of plagiarism.
However, presenting common knowledge without citing a source is generally not considered plagiarism. Common knowledge includes facts that are widely known and easily verifiable, such as the law of gravity. In academic writing, it's accepted that such information does not require citation since an educated adult is expected to be familiar with these facts.