Language is :

Correct option is A

a system of systems.
Language is often described as 'a system of systems.' This reflects the complex and hierarchical nature of language, encompassing various subsystems such as phonology (sounds), morphology (word formation), syntax (sentence structure), semantics (meaning), and pragmatics (language use). Each of these subsystems is complex in its own right but also interrelated, working together to enable communication and understanding.