A would be the correct answer because but has a comma has it before it.
I think that #3 is A #4 is B #5 is B #6 is D
A)
Ethos and logos
Ethos refers to the credibility of the speaker and his
knowledge about the subject. In the example given, the speaker is Dr. William
Leu who has attained a reputation and can be considered an expert about the
organ, heart, as he has over 25 years of experience being a cardiologist.
Logos refers to the message’s logic and backed up with
evidences. In the example given, Dr. Leu has researched and has a conclusion
about the topic, that’s why his claim can be considered as sufficiently backed
up.