What are the main characteristics of XML?

XML has the ability to define custom tags and hierarchical structures that allow for logical and coherent organization of information.
XML has a rigid syntax, similar to programming languages.
XML only allows for the creation of poorly formed documents.
XML is a closed standard that cannot be used by different applications.
a) Only statement I is correct.
b) Statements I and II are correct.
c) Statement I is correct and statements III and IV are incorrect.
d) Statement I is correct and statements II, III and IV are incorrect.