Mary is a little girl. She is only four. She is not at school. She doesn't know how to read or write. But her sister Joan is a schoolgirl. She is ten years old. She knows how to read and write. One day, Joan sees her little sister in the room. She's at the table. There's a pencil in her hand. She's writing. “What are you writing, Mary?” She asks. “I'm writing a letter to my friend Rose. ” “But you don't know how to write. ”says her sister. “Well,” says Mary, "it doesn't matter. Rose doesn't know how to read. "

读我国东部雨带移动示意图，回答下列各题。

下图为真核生物细胞核内转录过程示意图，下列说法正确的是（   ）