Which of the following is NOT an example of plagiarism in a written assignment?

a.
using the same ideas or arguments as another author but changing the wording slightly

b.
citing a direct quote but not using quotation marks around the quoted material

c.
discussing information that is considered "common knowledge" but not attributing that knowledge to a source

d.
using quotation marks around a direct quote but not citing the source of the quoted material

e.
using the same sentence structure or paragraph structure as another author but changing the wording slightly