一个关系中属性个数为1时，称此关系为 ( )。

A．对应关系

B．单一关系

C．一元关系

D．二元关系

WebSQL is a SQL-like （） language for extracting information from the web. Its capabilities for performing navigation of web （） make it a useful tool for automating several web-related tasks that require the systematic processing of either all the links in a（） , all the pages that can be reached from a given URL through （） that match a pattern, or a combination of both. WebSQL also provides transparent access to index servers that can be queried via the Common （） Interface.

WebSQL is a SQL-like （） language for extracting information from the web.

A．query

B．transaction

C．communication

D．programming