We should keep on ______ English every day to improve our spoken English.[ ]

A. to practice to speak  

B. to practice speaking  

C. practice to speak  

D. practicing speaking

一辆载重汽车及所载的货物共重4.9×10⁴N，当行至某桥头处，司机发现桥头上矗立着提示牌，如图所示，请你通过计算说明这辆车能否在该桥上安全驶过？若汽车以20m/s的平均速度行驶，则该汽车行驶到贵阳市需要行驶多少小时？