板状铸钢件，不设外冷铁时，两个冒口之间的有效补缩距离为铸件壁厚的（）。
A.两倍
B.2.5倍
C.4倍
D.4.5倍
参考答案：C
什么是液压传动
In educational settings "depends on others to do his/her work" is often preferred to "______".
A. cheats in exams B. fails to do one’s homeworkC. fails to do one’s schoolwork well D. cheats in class
