关于光的色散说法正确的是(    )

B

    Fraser is four years old. He has autism(自闭症). He lives in his own world. Everything is very difficult to him. He doesn't want to play with other children. He doesn't want to say any words to others. His parents are worried about him.

    Then Billy, a cat, comes. It helps Fraser go out of his world.

When Billy sees Fraser, it runs to him quickly. It sits beside Fraser with its paws on Fraser's legs. They seem to be old friends. Fraser says, "This is our cat. He can come to live with us." "I know our life changes," says Fraser's mother.

    Billy stays with Fraser all the time. They play together, listen to the story together and sleep together. When Fraser walks in the garden, Billy is never far away. When Fraser is unhappy, it always lies beside him.

    It seems crazy. But Billy is like Fraser's angel. Fraser changes a lot. The doctor says he is getting better. He doesn't have to see the doctor now.