Whenever you use other writers' ideas, however, you must acknowledge your sources. Doing so allows you to distinguish between your ideas and those of others; it directs your readers to relevant sources; and it allows you to give credit where credit is due. It is important to properly reference and cite your sources to avoid plagiarism and to give credit for original ideas.
Putting source material in your own words shows readers that you have a true understanding of that material. Also, to restate in your own words the full meaning of a phrase or passage helps readers understand difficult, complex, jargon-riddled or ambiguous passages.
The correct answer is: Option A. Adopt the horses.
Given the context in the excerpt stating the individuals that would be "taking possession of the new horses" are official U.S. Marines, it can be inferred that this practice will take place within legal bounds, and therefore "stealing the horses" is out of context in this case. The intent of this activity is to use the horses as part of the Marines' activities, and as such, it is clear the Marines are planning to "adopt" the horses, not "borrow" them.
