Final answer:
The passage identifies the 'speaker's credentials' which is part of a persuasive speech, showing the speaker's expertise to establish credibility and providing an appeal to ethos. The correct answer is option D.
Step-by-step explanation:
When analyzing the passage "A psychologist with a background in therapy explains cognitive behavioral therapy," the portion of the persuasive speech being determined is the speaker's credentials. This reflects the expertise and background of the speaker in the subject matter, which is used to establish credibility with the audience.
Features of the source of a persuasive message, such as the credibility of the speaker, are known to have a strong impact on the effectiveness of persuasion. The speaker's professional background in psychology serves as an appeal to ethos, which aims to convince the audience of the reliability of their perspective and the information being presented.