Dear friend,
    I am a girl from Beijing. I am a quiet girl. I like reading books. I want to be your friend. Now let me introduce my family to you. I have a good family. My father is tall and thin. He is a math teacher. My mother is a nurse. She likes reading books. My brother is a university student. I love my family very much. Welcome to my home.
                                                                                                                                                                                             Yours,
                                                                                                                                                                                               Li Xin

当我国各地白昼时间最长时，下列四幅图所示气压带、风带分布正确的是（    ）