single flank gear rolling tester

例句：

1. 1.This is a single room apartment.
   这是一间单间公寓。
2. 2. He has only one friend in the world.
   他世上只有一个朋友。
3. 3.The single mother had to work two jobs to make ends meet.
   这位单身母亲不得不做两份工作来维持生计。