Six-Year-Old Alex and 11-Year-Old Leah Watched Rachel Take Apart a Craft

Six-year-old Alex and 11-year-old Leah watched Rachel take apart a craft. Rachel then challenged them to put the craft back together from memory. Because Leah could put together the craft in her mind and then remember what it looked like, she has no problem reconstructing the craft. However, Alex had great difficulty with the challenge. Because he couldn't put it back together in his mind, he couldn't remember what the craft looked like before Rachel took it apart. Which of the following statements is true?

A) Leah is in the stage of concrete operations and has demonstrated reversibility.
B) Both Alex and Leah are in the stage of formal operations and have demonstrated naïve idealism.
C) Alex has clearly attained the cognitive of conservation, but Leah has not.
D) Both Alex and Leah have demonstrated conservation, which places them in the stage of concrete operations.