In recent years，with more and more cars onthe road, flying robots are used to deliver(递送)mails.Flying robots can1mails to people's houses without having todeal with heavy2. But they will spend too much time inreturning. A research center is trying to improve its flying robots with the3 ofhoming pigeons (信鸽).
Homing pigeons are pigeons that are4trainedto fly home from somewhere else. In tests, researchers5thathoming pigeons were6efficient(高效的)than flying robots at returning to their home. So the research center is tryingto use a flying robot, together with a7,to deliver mails. After the robot finishes its tasks，itcan8the pigeon back in the shortest possibletime.
Although it will cost more money to9pigeons,the research center says that it can10time. And the time it saves will make upfor the cost.
