The correct answer is (a) Dehradun.
Dehradun is the most urbanized district in Uttarakhand. It is the capital of Uttarakhand and is located in the Garhwal region of the state. The city has a population of over 1 million people and is a major tourist destination. Dehradun is also home to a number of educational institutions, including the Indian Institute of Technology Roorkee and the University of Dehradun.
Nainital is a city in the Kumaon region of Uttarakhand. It is a popular tourist destination and is known for its scenic beauty. The city has a population of over 300,000 people.
Haridwar is a city in the Haridwar district of Uttarakhand. It is a major Hindu pilgrimage site and is located on the banks of the Ganges River. The city has a population of over 200,000 people.
Almora is a city in the Almora district of Uttarakhand. It is the headquarters of the district and is located in the Kumaon region of the state. The city has a population of over 100,000 people.