flat magnetic field

例句：

1. 1. The floor is flat and smooth.
   地板是平坦光滑的。
2. 2. Thetable is flat enough fora group of people to sitaround it.
   桌子足够平坦，可以供一群人围坐。
3. 3. The road is flatand easy to drive on.
   这条路平坦且易于驾驶。