题目

没有细胞壁的细胞是（ ） A．酵母菌                B．细菌        C．绿色植物的细胞        D．神经细胞 答案：D 解析: 略Only when I got here _________ that I had made a big mistake.  A. did I realize      B. I realized     C. I have realized D. have I realized