启动二氧化碳回收系统时，应先启动（）。
A.制冷压缩机
B.低压压缩机
C.高压压缩机
D.制冷压缩机加热管
参考答案：D
—When did the famous writer die?
—In 1988. He ______ for twenty years. [ ]
A. has died
B. has been dead
C. died
D. is dead
