Billy Dengler, a 14-year-old boy, is in the eighth grade. A month after he was born, Billy's mother, Terri, noticed that his eyes weren't quite as big as a normal baby's. She took Billy to the hospital, and the doctor said Billy would never be able to see. Although Billy can't see, he has never let that hold him back or make him different. Billy began teaching himself computer programming by using a screen reader when he was just seven years old. He is a certified Google developer   now. Google even tried to offer him a job last year when he discovered a problem in one of its _ , but Billy wasn't old enough. Billy's dream school would be Stanford University or MIT, where he could get a very good education in computer science. After he leaves school, whether he will go to work at a company like Google or design a software company of his own is still to be decided. However, he says he will definitely   do something great. "It's a sighted world," Billy said. "You can't let anything get in the way of your dreams, and if you do that, you can't move forward and make your dreams come true." Billy started to learn computer programming by himself with the help of  _  .
a screen reader his mother a computer his teacher