对铸件进行落砂清理时，应注意什么事项？（）
A.直接伸手测试铸件温度
B.直接伸手测试型砂温度
C.戴好防护手套再进行落砂清理
参考答案：C
_____ him speak English so fluently, and you would think him an American.
A．Hearing
B．Hear
C．Heard
D．Having heard
程序控制按程序可变性分类有哪些？
