The correct answer is (a).
Constitution Day is celebrated in India on November 26 every year. It is the day on which the Constitution of India was adopted in 1949. The Constitution of India is the supreme law of the country and it sets out the fundamental rights and duties of citizens, as well as the structure and powers of the government.
Option (b) is incorrect because November 27 is not Constitution Day.
Option (c) is incorrect because January 26 is Republic Day. Republic Day is the national day of India and it celebrates the adoption of the Constitution of India.
Option (d) is incorrect because August 15 is Independence Day. Independence Day is the national day of India and it celebrates the day India gained independence from British rule.