双氰胺结构简式如图．

（1）双氰胺的晶体类型为 ____．

（2）双氰胺所含元素中， ____ （填元素名称）元素基态原子核外未成对电子数最多．

（3）双氰胺分子中σ键和π键数目之比为 ____

    When I was in the seventh grade, I was a volunteer at a local hospital in my town.Most of the 1 I spent there was with Mr. Gillespie.He never had any visitors and nobody seemed to care about his 2.

    I spent many days there holding his hand and talking to him,3 anything that needed to be done.He became a close friend of mine,4 he responded with only an occasional squeeze(捏) of my 5. Mr. Gillespie was in a coma(昏迷).

    I left for a week to vacation with my parents, and when I came back, Mr. Gillespie was 6. I didn't have the7 to ask any of the nurses where he was, for fear that they might8 me he had died.

    Several 9 later, when I was a senior in high school, I was at the gas station when I noticed a familiar face.When I10 who it was, my eyes filled with tears.He was 11! I got up the nerve to ask him if his name was Mr. Gillespie. With an uncertain look 12 his face, he replied yes.I 13 how I knew him and that I had spent many days talking with him in the hospital.His eyes welled up with tears, and he gave me the warmest hug I had ever 14.

    He began to tell me that15 he lay there comatose(昏迷的), he could hear me talking to him and could 16 me holding his hand the whole time. Mr. Gillespie17 believed that it was my voice and 18 that had kept him alive.

    Although I haven't seen him since, he fills my heart with 19 every day.I know that I made a(n)20 between his life and his death.

（$-\frac{27}{8}$+____ ）÷（-7）²=0

下图漫画启示我们青少年要（）