fixed neutral density filter

例句：

1. 1. The design is fixed and cannot be changed.
   设计是固定的，不能更改。
2. 2. The date for the meeting has been fixed.
   会议的日期已经确定。
3. 3. The team's strategy was fixed before the game started.
   比赛开始前，团队的策略就已经确定了。