normal speed

例句：

1. 1.The car is moving at a normal speed on the highway.
   汽车在高速公路上以正常速度行驶。
2. 2. The train is running at its normal speed.
   火车正以正常速度运行。
3. 3.The plane is flying at its normal speed.
   飞机正以正常速度飞行。