中间等级

例句：

1. 1.The middle of the road is the safest place to cross.
   路中间是过马路最安全的地方。
2. 2. The middle of the book is where the story starts.
   书的中间是故事开始的地方。
3. 3. The middle class has more opportunities than the lower class.
   中产阶级比下层阶级有更多的机会。