Copyright law is surprisingly simple in most cases involving text. The writer (or in some cases, the publisher) owns the text he or she wrote. If you did not write it, then you do not own it. If you do not own it, you cannot use it in a way that fails to give credit to the owner.
It's sort of like renting a car. You would be lying if you told someone that you owned the car. Of course you are able to use the car, but it is not yours.
A journalist is expected to provide clear and true attribution for all sources, including copied text. It does not matter if you copied it from the Internet or from a newswire service. It is not yours. Don't pretend it is.
Journalism educators realize that some students say, "What's the big deal? It's only a homework assignment." We are trying to train you for real jobs in journalism. If you violate the ethics of journalism on the job, you could be fired.
It's neither ethical nor acceptable for you to steal other people's text in your homework assignments.
While some cases of dishonesty in journalism involve plagiarism, other cases involve other ways of misrepresenting the truth. These include: