A、A brain injury. B、A slight accident. C、A miserable childhood. D、A regular nightmare. A

Close your eyes. Picture your closest friend. Maybe you see her blue eyes, long nose, brown hair, perhaps even her smile. If you saw her walking down the street, it would match your imagined vision. But what if you saw nothing at all? James Cooke, 66, can’t recognize other people. (16) When he meets someone on the street, he offers a "hello" because he can’t be sure if he’s ever met that person before. "I see eyes, nose, cheekbones, but no face," he said. "I’ve even passed by my son and daughter without recognizing them." He is not the only one. (17)Those with face blindness can see perfectly well, but their brains are unable to piece together the information needed to understand that a collection of features represents an individual’s face. The condition is a neurological mystery, but new research has shed light on this strange malady. One of the keys to understanding face recognition is understanding how the brain comes to recognize voices. (18)Some scientists had believed that faces and voices, the two main ways people recognize one another, were processed separately by the brain. But by testing for these two conditions simultaneously, researchers at the Max Planck Institute for Human Cognitive and Brain Sciences in Germany recently found evidence that face and voice recognition may be linked in a novel person-recognition system. It is unclear how many people have these conditions. Many don’t even realize they have problems with face or voice recognition. (19)While some develop these difficulties after a brain injury, others develop it in childhood.
16. Why does James Cooke say "hello" to someone on the street?
17. What can we learn about people with face blindness?
18. What did some scientists once believe?
19. What may cause face blindness?