常见的止回阀有旋启式、多瓣式和()式三种。
参考答案:微阻缓闭
Everyone in our class was working hard and doing what we could ______ a good college.[ ]
A. enter
B. to enter
C. entering
D. entered
直眼掏槽时眼的深度不受巷道断面限制,可以进行()爆破。