A car is traveling at a speed of 30 m/s. If the car decelerates uniformly at a rate of 5 m/s^{2} for a distance of 80 meters, what is its final speed? 
选项为:A:5 m/s  B:10 m/s  C:20 m/s  D:30 m/s  请回答其中一个选项.