speed不是不可数嘛,那么at a high speed 又怎么说呢、、、

speed不是不可数嘛,那么at a high speed 又怎么说呢、、、 with a high speed 还是at a high speed? at high/fast speed at high speed 还是at a high speed,教材上是前一种 at speed 还是at a speed High-speed AT FULL SPEED和at high speed的区别. It's reported that this high-speed （ ）at speed of 417 km/h A At a fantastic speed is dangerous _a car at such a high speed. what a high speed he is runing at at high speed 和with great speed 有什么区别?