The idea of natural language access to a database is not new，21_____ still hasn’t been achieved. Most search engines are not able to 22_____ questions such as “Where can I get light bulbs?” or “ 23_____ legs does a horse have?” The answer 24_____ the questions can be found for certain on the Web， but the search engines are not able to understand the questions. 25_____ you have a page that has a question and an answer on it， then you may succeed， but this is a 26_____ case. Instead of receiving the answer “At shop XY in Z” or “four”，you would receive a long list of search 27_____ ， as the search engines split up the question into 28_____ . Every word in the question is then searched 29_____ .
The 30_____ between conventional and natural language search engines is the way pages get indexed. Unlike a conventional database, the symbolic approach to natural language processing involves treating words as nodes in a semantic network. The emphasis is then placed on the meaning of the words instead of the single words.
21.
A.and B.rather C.also D.but正确答案D
