WebSQL is a SQL-like (1)language for extracting information from the web. Its capabilities for performing navigation of web (2)make it a useful tool for automating several web-related tasks that require the systematic processing of either all the links in a(3),all the pages that can be reached from a given URL through (4)that match a pattern,or a combination of both. WebSQL also provides transparent access to index servers that can be queried via the Common (5)Interface.

空白（3）处应选择（）

A.hypertext

B.page

C.protocol

D.operation

案头研究是采购市场研究的主要信息来源。