阅读下列材料，从A、B、C、D四个选项中选出最佳答案。

Kate is a little girl. She's only five. She is not at school. She doesn't know how to read or write. But her sister Mary is a student. She knows how to read and write.

One day, Mary sees her little sister in the room. She is at the table. There is a pencil in her hand. She is writing. "What are you doing, Kate?" She asks. "I'm writing to my friend Rose." says Kate. "But how can you? You don't know how to write." says her sister. "Well," says Kate, "it doesn't matter(关系). Rose doesn't know how to write, either.