round horizon

例句：

1. 1. The moon is always round at full moon.
   满月时月亮总是圆的。
2. 2. The ball was round and smooth.
   球是圆的，光滑的。
3. 3. The car circled the block twice before we reached our destination.
   汽车在到达目的地之前绕街区转了两次。