Final answer:
Plagiarism is illegal due to intellectual property theft, evaluating sources requires checking credibility and relevance, and imposing modern values on history can misrepresent context.
Step-by-step explanation:
Plagiarism is against the law because it involves the unauthorized use and theft of someone else's intellectual property, often leading to the misrepresentation of one's own work. Dealing with sources, it is important to consider competing sources about the same topic to gain a comprehensive understanding and to develop critical thinking skills. Assessing the trustworthiness of a library book can be done by checking the author's qualifications, the publisher's reputation, citations, and the date of publication.
When evaluating online resources, it's crucial to identify if the source is reliable by considering author expertise, domain credibility, and cross-referencing information. Lastly, applying modern values to historical events can result in an anachronistic understanding, thereby distorting the perception of those events and potentially leading to incorrect conclusions or misrepresentation of historical context.