题目

When I was a young boy of 6 , I lived with my grandparents in the country and my grandfather had a bicycle. Because of my grandfather’s   36   about my possible hurt by riding the bicycle, I wasn’t  37 to ride it. However, the big bicycle   38___ me  greatly. One day, I got on it and rode away. Back then, I was  39  enough—I didn’t know what fear was—and loved to try  40  things. Slowly I rode the bicycle along a road   41   the small hill behind our village. When  I got to the top, I stopped .I  42  to ride down the hill. In my opinion, it would be very exc现有（NH4）2CO3、（NH4）2SO4、Na2CO3、Na2SO4 四种白色粉末，请设计实验加以鉴别．