The definition of plagiarism as presented by The Brief New Century Handbook, $2$ nd ed$.$ is "Plagiarism is defined as the unauthorized or misleading use of language and text of another author."

You're plagiarizing if you...

d$.$ All of the above

a$.$ Buy a paper from an Internet site, another student or writer, or any other source and pass it off as your own.

b$.$ Turn in a paper that someone else has written, whether the person has given it to you, you've downloaded it from the Internet, or you've copied it from any other source.

c$.$ Changed selected parts of an existing paper and claim the paper as your own.