This question is about which country marked 70 years of diplomatic ties with India through a stamp featuring the Ramayana. Bangladesh, Sri Lanka and India can be set aside together, since none of them released this particular commemorative stamp in 2019, and India was the counterpart nation rather than the issuer.
Indonesia is the country that actually issued the stamp, a gesture that highlights how deeply the Ramayana is woven into Indonesian culture, especially in Bali and Java, despite Indonesia being a Muslim majority nation.
So the correct answer is Indonesia.
What makes this fact memorable, and what the question is testing, is the seeming contradiction of a Muslim majority country choosing a Hindu epic to mark a diplomatic milestone. Working through each option with that in mind clarifies the choice.
Once the cultural surprise is traced back to its actual source, it points squarely to Indonesia rather than to the countries where a Ramayana connection might seem more obvious.
Therefore, the correct answer is Indonesia.