Mildred Webinga Freeman was an English teacher at the new middle school I attended in the ninth grade.She wasn't my1;she was the adviser to the safety patrol（巡逻）on which I2.I loved being around her and3her sense of humor and kind personality.She was4a good listener.

    At the end of the year,she5that she was moving to Florida,and I was very sad.We exchanged6and became pen pals.I could tell her7,and she treated me8respect even though I was a teenager.

    In Florida ,Mrs. Freeman became a Realtor（房地产经纪人）,9she managed to find time to write letters.She wrote10stories and always took my concerns11.She had given me a(n)12invitation to visit,and I missed her so much.When I13to take her up on the14,she answered,"Get your shoes on and your bags15!You are welcome anytime!"

    I spent three weeks with her in Miami.Her16of poetry,music,and creative writing17me to follow these endeavors（努力）.One day18hanging sheets on the clothesline,she19and said,"You know,the sky is fuel for the soul."I had never looked at the20before hearing those words.Later that year,I received a call that Mrs.Freeman had died.

水是一种重要的自然资源。下列对水的认识正确的是（）