任务型阅读，阅读下面短文，并用英语回答问题(请注意每小题后面的词数要求)。
Mr. Beynolds, my teacher, handed us a list of thoughts, and asked us to write a paper on one of those thoughts. I chose the topic “I wonder why things are the way they are.”
I wrote down all the questions that puzzled(困扰) me about life. I realized that many of them were hard to answer, and perhaps others could not be answered at all. When I handed in my paper, I was afraid that I might fail because I did not answer the questions.
The next day, Mr. Reynolds handed me the paper and asked me to read it for the class. The other students became quiet as I began to read my story:
Mum, why are the roses red? Why is the grass green and the sky blue? Why do I have to graduate(毕业)? Why do I have to grow up? Why do I have to be called “Grandma” on day? ...
Dad, why can't I stay out until 12:00? Why do I miss my old friends? Why do I miss being at home? Why do you love me so much? ...
Mum, Dad, why did you have to leave me? I need you.
At the end of my story, I looked at Mr. Reynolds, and I saw a tear slowly coming down his face. Then I realized that life is not built on the answers we receive, but on the questions we asks.
中，能大量共存的一组离子是( )
