当前Internet使用的IP协议是在网络中( )次上使用。

A．应用层

B．网际层

C．数据链路层

D．运输层

XML is a (71) language for documents containing (72) information.

Structured information contains both content(words, pictures, etc.)and some indication of what role that content plays(for example, content in a section heading has a different meaning from content in a footnote, which means something different than content in a figure caption or content in a database table, etc.). Almost all documents have some structure.

A markup language is a (73) to (74) structures in a document. The XML specification defines a standard way to add markup to (75) .

（72）处填（）。

A．struction

B．structrual

C．structure

D．structured