题干
Not until ________a third time ________that he had given birth to the reading system for the blind called Braille.
| A．Louis Braille tried；he announced |
| B．did Louis Braille try；he announced |
| C．Louis Braille had tried；did he announce |
| D．had Louis Braille tried；had he announced |
答案(点此获取答案解析）
