题目

 — You look tired.   — Yes, I ______ non-stop until seven o'clock. A. had worked             B. would be working          C. was working         D. have been working 答案：C在细胞周期的哪一阶段合成为新细胞的建成所需要的蛋白质？ A．在前期的开始    B．在S期前    C．在前期之末