Final answer:
A signal phrase is used to introduce material from sources, indicating who wrote or said the information. The correct option is B.
Step-by-step explanation:
A signal phrase is primarily used to let the reader know who said or wrote what you are about to share. It's a useful strategy in essay writing, more so when integrating sources and quoting or paraphrasing other author's work. For example, you might write, 'According to Professor Johnson, ...' or 'As Shakespeare wrote in his play, ...'. This choice corresponds to option B in your question.
Learn more about Signal Phrase