Final answer:
Copying verbatim without giving credit is the only option from the list that constitutes plagiarism, while quoting with citation, paraphrasing with attribution, and summarizing with credit given are all ethical practices.
Step-by-step explanation:
When people prepare speeches, it is possible for them to commit plagiarism (intellectual theft) in various ways. The correct choice from the provided options is c) Copying verbatim without giving credit. This action constitutes plagiarism because it involves taking someone else's words or ideas and presenting them as your own without appropriate acknowledgement. In contrast, a) Quoting accurately with proper citation, b) Paraphrasing with attribution, and d) Summarizing information from multiple sources, are all ethical ways of incorporating outside information into a speech as long as proper credit is given to the original authors. It is crucial to properly cite sources to establish credibility and avoid the unethical practice of plagiarism.