Which of 3 year-old Sarah's activities provides the best example of the symbolic function substage of preoperational thought?
1) She takes a crayon, scribbles a big blob on a piece of paper, and says, 'That's you, Mommy!'
2) She says, 'When Mommy leaves my room, I know that she's still in the house!'
3) She actively searches for her favorite toy, even though it is partially covered by a blanket.
4) She is making cookies and says, 'Those two cookies have the same amount of dough, even though one is thicker than the other.'