内容摘选：
Book 1
1. Where Does Milk Come from?
Billy is six years old.
He visits his uncle and aunt every summer.
They live on a farm.
They have cows, chicken, sheep, and a big horse on the farm.
Billy loves all the animals.
This summer, he is going to learn how to mild a cow.
Wow! His friends cannot believe it.
"We get our milk from the store," they say. "But our friend is going to get it from a cow."
Billy laughs. "Milk does not come from the store," he says. "Milk comes from a cow."
His friends do not believe him.
But his teacher says, "Yes, milk comes from cow.
Cow eat grass. They change the grass into milk.
The farmer sells the milk. And we buy it in the stores."
The teacher tells them one more thing.
"Did you know that cows have four stomachs?"
The kids are surprised. But it's true!
……
