The paper introduces the design course of the modular machine tool for multi-holeconcentration gearbox.
介绍了多孔密集型箱体组合机床的设计过程，实际证明该机床设计严谨规范，又有技术创新，使用效果良好。
2
Most astronomers believe that the large concentration of mass at the galaxy's center is a black hole whose gravity is causing the gas to whirl.
大多数天文学家认为，星系中心的大量物质是一个黑洞，它的引力导致气体旋转。
3
The hole isn't literal; no part of the stratosphere is empty of ozone. But scientists use the hole metaphor to describe the area where ozone drops below a historical concentration of 220 Dobson Units.