催化剂碳堆积的现象是（）。
A、再生催化剂含碳量减少
B、再生器稀密相温差增加
C、再生器旋风分离器压降减少
D、反应压力明显下降
参考答案：D
Tina _____ have known the truth, or she would have told us.
A．mustn't
B．shouldn't
C．can't
D．needn't
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