???  ??? A traffic police officer holds a pilotless airplane in his hand. The 1.8-kilogram pilotless airplane has a diameter of 50 centimeters and has been used at the high-tech fair to help traffic police monitor road conditions. Video from the plane is instantly sent to traffic police via a 3G network. Inset: The pilotless airplane flies above Shenzhen Convention and Exhibition Center on Thursday, a day ahead of Friday’s opening of the China Hi-Tech Fair that continues through Wednesday. Lin Qingrong | 