铸件的壁厚较小时，由于冷却速度快，冒口的有效补缩距离就大。
参考答案：错
23．Robert made a call to his parents yesterday afternoon. To his disappointment, ____of them answered it.
A．either
B．both
C．none
D．Neither
叙述滤饼起疙瘩的原因和处理方法？
