Plz help me, fast! Which statement about signal phrases is true?

Select one:

a. Signal phrases should be worded the same way throughout an informational text.

b. Signal phrases are only needed when a writer uses a direct quote from an article.

c. Signal phrases should provide just enough information to show the reader that the source is a valid one that can be trusted.

d. Signal phrases should provide name, job, and source of every fact used in a text.