下列物质的转变中，不能只通过一步反应实现的是 （　）                       

B

    I have a twin brother, Bob. He is taller than me. His hair is shorter than mine. Many people think we must have many things in common. But in fact this is not true. Bob is more outgoing than me. When my parents' friends come to our house, Bob often sits there and talks to them. But I often sit there and say nothing. Bob likes reading, cooking and drawing. I just like swimming and playing basketball. He has more hobbies than me, but he is not as athletic(擅长运动的) as me. Because Bob does better than me at school, my mom often says to me, “Bob is younger than you, but he can get better grades, you should learn from him.” We both like eating fast food and listening to music.

如图，若在象棋盘上建立直角坐标系，使“将”位于点（0，﹣1），“象”位于（2，﹣1），则“炮”位于点（　　）