Which of these is a clue that the author is a reliable source about how teenagers feel when they don't get enough sleep?
A) He is a school official who sees the effects of lack of sleep on teenage students.
B) The author is in the 10th grade, so he's a teenager who knows the topic firsthand.
C) He is writing about a topic that only a doctor, a scientist, or a health expert could possibly understand.
D) The title "Professor" comes before his name, so he must know a lot about teenagers.