In recent years, with more and more cars on the road, flying robots are used to deliver (递送)mail. Flying robots can 1 mail to people's houses without having to deal with heavy 2. But they will spend too much time in returning. A research center is trying to improve its flying robots with the 3 of homing pigeons (信鸽).
Homing pigeons are pigeons that are 4 trained to fly home from somewhere else. In tests, researchers 5 that homing pigeons were 6 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 a 7, to deliver mail. After the robot finishes its tasks, it can 8 the pigeon back in the shortest possible time.
Although it will cost more money to 9 pigeons, the research center says that it can 10 time. And the time it saves will make up for the cost.
