In recent years, with more and more cars on the road, flying robots are used to deliver（递送） mails. Flying robots can1 mails to people's houses without having to deal with heavy2 . But they will spend too much time in returning. A research center is trying to improve its flying robots with the3 of homing pigeons 信鸽）.
Homing pigeons are pigeons that are4 trained to fly home from some-where else. In tests, researchers5 that homing pigeons were6 efficient（高效的）than flying robots at returning to their home. So the research center is trying to use a flying robot, together with a7 , to deliver mails. After the robot finishes its tasks, it can8 the pigeon back in the shortest possible time.
Although it will9 more money to raise pigeons, the research center says that it can10 time. And the time it saves will make up for the cost.
