Totally 4 combustor groups are there at the front and back of boiler.
锅炉前后各有两组燃烧器，每三个燃烧器为一组，共有4组。
2
Before long, quite a lot of boiler-plate code is devoted to mapping the application domain model into Lucene data structures and getting it back out again.
在之前很长一段时间，相当多的样板式代码热衷于把领域模型映射到Lucene数据模型上去。
3
In order to save space, the back of the boiler had been let into the wall.