Question: A teacher introduces a token system to increase a student's reading fluency using an A-B design. The student's fluency improves. Which is the best reason the teacher cannot conclude that the token system was the cause? Group of answer choices a) Fluency is not measurable in single-case designs. b) Confounding events could have coincided with the intervention. c) A-B designs require at least three baseline phases. d) Tokens are not valid reinforcers in applied work. Need Assignment Help?