阅读理解

    My problems started after I went to a boarding(寄宿)school. I was only 14, and at first I missed my family a lot. I often called them and cried on the phone. But after two weeks, I found I enjoyed being with my classmates at school. I had many friends who were boys. I thought of them as my best friends-but only friend. I never guessed my friendship with boys would become a problem.

    Then, two months later, my friends told me that some teachers and girls said I was hanging out with boys all day long to get attention(注意)from them. A few months after that, the class teacher James asked the class to choose some students to join the Student Union. I thought I could win for I was doing well at school. I came first in the English and Math exams. A week later, the list(名单)came out and it didn't include me. James came to me and said, "Don't be sad. I know you're excellent! Maybe you're a little distant(远的)from the girls in our class. They don't know much about you, so some of them didn't choose you. It doesn't matter. Do your best to get on well with everyone and I think you'll make it next time. "

在不损坏高等植物细胞内部结构的情况下，下列哪种物质适用于除去细胞壁（    ）