Sheila is in fourth grade but is still reading at the first-grade level. She has normal intelligence and is able to understand concepts and contribute to class discussions. When Sheila is given a written quiz, however, she hands in a blank paper. Which of the following best describes Sheila's underlying difficulty?
a) Sheila has autism.
b) Sheila has an intellectual disability.
c) Sheila has a behavioral disorder.
d) Sheila has a learning disability