teachers' room;the teachers'room.this is ()room,这里应该选哪个?

teachers' room;the teachers'room.this is ()room,这里应该选哪个?
为什么有些人说加the 有些人说不加the ,我都搞不清楚了,还有heavy traffic是要加冠词的吗?他可不可以加any,或者some?；have ( ) intrest in,括号中是填an,还是the ,还是零冠词?；belief加了s之后才是信仰的意思,还是不加s也有信仰的意思?