Step 1: Meaning:
Ethno-national means an ethnic group that sees itself as a nation. We need the factors that bind such groups together and make them ask for recognition.
Step 2: List common markers:
The common markers in the Indian setting are a shared mother tongue, a shared homeland or region, and a shared tribal heritage.
Step 3: Treat religion separately:
Religious identity in India is normally studied under communalism, which is a related but different topic. So religion is set aside from this list.
Step 4: Compare with the options:
Dropping B leaves A, C and D. Only option 3 has exactly these three.
Step 5: Closing check:
Options 1, 2 and 4 all include B, so they cannot be right under this reading.
Cross-check:
To be careful, we can also see why a different reading might not fit the textbook. The usual textbook lines say that regional, linguistic and tribal identities have each led to demands for recognition within the Indian Union, while religious identity is taken up under communalism and secularism. This is a judgement based on the course material, so the answer rests on that standard grouping. On this grouping the three bases are language, region and tribe, and the answer stays option 3.
Final Answer:
The answer is option 3.
\[\boxed{\text{A, C and D only}}\]