下列物质属于纯净物的是（）

Dear friends,
   My name is Helen. I'm 12 years old. I  1  from Taxas, America. I’m really  2   in Chinese geography. It's fun! And I hope you can tell me more. I like hamburgers best,  3   I try to eat them twice a week  4   it's a kind of   5   food. And I like to drink lemon  6   . As for sports, I often go swimming with my parents on weekends.
   I   7  in Cobb Street School. My   8  subjects in school are ME and art. They are really fun! After school, I like to go to the   9   with my family or friends. I like action movies and cartoons. They’re  10   How about you? Do you often go to the cinema with your family or friends?
                                                                                                                                                                   Yours,
                                                                                                                                                                   Helen

植物的种子结构中的胚轴将来发育为植物的茎。