Many modern search engines for information retrieval system retrieve a large number of documents from a word-search query. Yet a simple question in natural language requests only an answer that is simple, accurate, and likely only one. A whole document of search result causes the inquirers to read through or find the answer in the document. Also too many documents in return distract the inquirers from their concern. We propose an idea of using knowledge machine to retrieve one finest answer for one-question-one-answer query. A search engine for natural-language application on medical field is introduced and its possible impact is discussed.