Tell the secret of bat flying at night in your own words 100 words

Bats fly at night and can catch moths and mosquitoes; And no matter how you fly, you have never seen it collide with anything. Even very thin wires can be cleverly avoided. Are your eyes so keen that you can see everything in the dark night? In order to find out this problem, scientists did an experiment more than 100 years ago. In a room, a lot of ropes were pulled at will, and many bells were tied to the ropes. They blindfolded the bat and let it fly in the house. The bat flew for hours, but no bell rang. It didn't touch any rope. Scientists have done two more experiments: one is to plug the bat's ears, and the other is to seal the bat's mouth and let it fly in the house. Bats bump around like headless flies, and the bells hanging on the rope keep ringing. Three different experiments have proved that bats fly at night, not by eyes, but by the combination of mouth and ears to find their way. After repeated research, scientists finally uncovered the secret that bats can fly at night. When it flies, it will make a sound from its mouth. This sound is called ultrasound. Human ears can't hear, but bats can hear. The ultrasonic wave moves forward like a wave, and when it meets an obstacle, it reflects back and reaches the bat's ear. The bat immediately changes its flight direction.