动物细胞与植物相比，不含____ 、____ 、____ 。

    Xie Lei ____ a plane for London six months ago to complete a business ____ .She is now halfway through the       3    year. At the beginning, she had to learn almost everything again. She lives with a      4    family, which gives her the         5     to learn more about everyday life and      6     in her new country.

    She wrote her first      7    to her        8     ， but she only got an E. Now she has    9    the life and she feels much more at home and is going to join a few university clubs in order to have a balance between study and a social life. We wish Xie Lei all the best with her    10   Keep it up! Xie Lei.

下列类别物质的组成中一定只含有两种元素的是（     ）