Four$-$year$-$old Jonathan is sitting at the table next to his $9-$year$-$old sister Erin. They are having hot dogs for lunch. When his mom cuts Jonathan's hot dog into five pieces and Erin's into six pieces, Jonathan complains, "Erin has more than me$!"$ Erin says, $"$no I don't, they are the same!" What concept does Erin understand?

Animism

Seriation

Egocentrism

Conservation