Eight-Year-Old Johnny and His Mother Are Making Cookies

Multiple Choice

Eight-year-old Johnny and his mother are making cookies. Johnny's mother gives him two pieces of dough that are rolled into balls. She asks him to take the rolling pin and roll one flat. Johnny recognizes that both pieces of dough are still of equal size. He has mastered conservation of

A) number.
B) length.
C) mass.
D) area.