常用刀具的材料种类有金属材料和（）两种。
参考答案：非金属材料
Mr.Smith was much surprised to find the watch he had had__________was nowhere to be seen.
A．repairing
B．it repaired
C．repaired
D．to be repaired
以原红和早幼红细胞增多为主的疾病是
A．慢性失血性贫血B．真性红细胞增多症C．骨髓增生异常综合征D．急性红白血病E．再生障碍性贫血
