Everyone faces challenges in their life， but some are more difficult than others． Daniel Kish had serious problems with his eyes when he was born． And doctors took away both of his eyes before he was fourteen months old．

Soon later， however，he started to do an amazing thing．He started to make clicking （咔哒） sounds with his tongue （舌头） to help him move around． Much like a bat （蝙蝠） ， he now moves about using sonar （声呐）． （1） 　　He and his group， World Access for the Blind， teach others how to use sonar．In this interview with National Geographic， Kish explains how sonar works．

How does sonar work？

"When I make a clicking sound， it makes sound waves． These waves reflect （反射） off surfaces all around and return to my ears． My brain then processes the sounds into images （图象）（2） 　　"．

When you click， what do you see in your mind？

"Each click is like a camera flash． I make a 3D image of the things around me for hundreds of feet in every direction．

What is it like riding a bike using sonar？

"（3） 　　I click up to two times per second， much more than I usually do"．

Is it dangerous to move around the world in this way？

"Much of the world lives in fear of things that we mostly imagine． I have a habit of climbing everything， but I never broke a bone （骨头） as a kid．"

How challenging is it to teach people to use sonar？

"Many students are surprised how quickly results come． （4） 　　It's in the mind"．

A． It's exciting and enjoyable but requires a lot of focus． B． He is so good at it that he can ride a bicycle in traffic． C． Seeing isn't in the eyes． D． It's like having a conversation with the environment．