The Great Wall, _____ to be the longest wall in the world, runs across China like a huge dragon.[ ]

A. saying        

B. to say      

C. said    

D. being said

160km/h以下区段接触网的拉出值标准值为（）。

A、0-250mm

B、0-300mm

C、0-350mm

D、0-400mm