Communicative language teaching stresses the interdependence of :

The correct option is Language and communication.

Step-by-Step Explanation:

1. Understanding Communicative Language Teaching (CLT):
Communicative Language Teaching is an approach to language teaching that emphasizes learning a language through genuine communication. Instead of focusing solely on grammar rules, vocabulary lists, or isolated structures, CLT prioritizes the learner's ability to use the language effectively in real-life contexts.

2. The Concept of Interdependence:
In CLT, language is not viewed as an abstract system of rules studied in isolation. Rather, it is seen as a tool used to achieve social and communicative purposes. Therefore, language proficiency and communicative competence are interdependent:
- We acquire and develop language by engaging in meaningful interaction and communication.
- Effective communication relies on a functional command of the language.

3. Analyzing the Options:
- Language and conversation: While conversation is a key part of CLT, communication is a much broader category that includes reading, writing, non-verbal cues, and formal exchanges, making "communication" the more accurate and comprehensive term.
- Language and behaviour / Language and psychology: These options relate to behavioral or cognitive theories of learning rather than the core instructional focus of the Communicative Approach.
- Language and communication: This directly captures the essence of CLT, which asserts that language learning happens through communication and that the ultimate goal of language learning is to communicate.