Question: The purpose of an XML schema is to define the building blocks of an XML document. Which option best describes the building blocks of an XML document?

1. Header files, function declarations, global variables with their data types, and system library folder location.
2. Namespace declaration, processor type, markup references, and encoding specification.
3. The document's elements and attributes, their data types and default values, and the number and order of child elements.
4. XML entity definitions, XSLT and cascading style sheets, DOM specification, and CDATA assignments.

Answer: The correct answer of the above question is Option C:The document's elements and attributes, their data types and default values, and the number and order of child elements.