如图，点P是菱形ABCD对角线BD上一点，PE⊥AB于点E，PE=4，则点P到BC的距离等于（　　）

某同学进行如下的实验：将一盆A植物放在暗箱内，而将B植物放在凿了一小洞的暗箱内，如图所示。几天后发现A植物向上生长，而B植物向小洞处弯曲掌长。此实验可以说明(     )

Dear Zhou Lan,   

    Thank you very much for your e-mail. I want to go to China. I know something about China from your e-mails. Your English is very good. But I don't know much Chinese. Now I'm learning (学习) it from my parents in the USA. They know much about China. They tell me many things about China.

    I'm happy to know you like your school and your family. You want to know my family and my school. I have a big family. My grandparents and my parents are all very fine. My father has a brother. He is my uncle, John. He and my aunt have their children. They're Bill, Linda, Mary and Lily. My brother Dick is a boy of eighteen. I like my family very much. I'll go to China next year with my mother. She is going to teach English in a middle school in Beijing.

Yours,

               Annie

Rose was angry with me. If only I________those words to her!