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 India and it provides for a parliamentary system of government. It also guarantees fundamental rights to all citizens of India.
Option (b) is incorrect because November 27 is not Constitution Day.
Option (c) is incorrect because January 26 is Republic Day. Republic Day is celebrated in India on January 26 every year to commemorate the adoption of the Constitution of India.
Option (d) is incorrect because August 15 is Independence Day. Independence Day is celebrated in India on August 15 every year to commemorate the day when India gained independence from British rule.