零件渗碳后，含碳量从表层到心部逐渐（）。
参考答案：减少
Tom, you play the violin so well. But I ______ you can play the violin.
A．didn’t know
B．don’t know
C．hadn’t known
D．haven’t known
简述肺炎的SARS症状、体征及临床诊断
