WebSQL is a SQL-like (26) language for extracting information from the web. Its capabilities for performing navigation of web (27) make it a useful tool for automating several web-related tasks that require the systematic processing of either ail the links in a (28) , all the pages that can be reached from a given URL through (29) that match a’ pattern, or a combination of both. WebSQL also provides transparent access to index servers that can be queried via the Common (30) Interface.

（29）是（）

A.paths

B.chips

C.tools

D.directories

单位体积内流体的质量称为该流体的（）。

A.比重

B.密度

C.重量