The correct answer is option D: Chandragupta Maurya. Let's delve into the details of this answer.

Chandragupta Maurya
Chandragupta Maurya was the founder of the Mauryan Empire, which was one of the largest and most powerful empires in ancient India. He ruled from 322 BCE to 298 BCE. Chandragupta Maurya was not only a powerful ruler but also a great strategist and administrator.

Ashoka
Ashoka, also known as Ashoka the Great, was the grandson of Chandragupta Maurya. He is considered one of the greatest rulers in Indian history. Ashoka ruled from 268 BCE to 232 BCE and is best known for his conversion to Buddhism and his efforts to spread the teachings of Buddha throughout his empire.

The Mauryan Empire
The Mauryan Empire, under Chandragupta Maurya and later Ashoka, extended over a vast area, including most of present-day India, Pakistan, Bangladesh, and parts of Afghanistan. It was a centralized empire with a strong administration and a well-structured bureaucracy.

Ashoka's Grandfather
Chandragupta Maurya was the grandfather of Ashoka. He laid the foundation for the Mauryan Empire and established the administrative and political systems that Ashoka later inherited and further developed. Chandragupta Maurya's conquests and administrative reforms set the stage for Ashoka's rule and his subsequent transformation as a Buddhist emperor.

Ashoka's Legacy
Ashoka is remembered for his policy of Dhamma, which emphasized moral principles, non-violence, and the welfare of his subjects. He erected numerous pillars and edicts throughout his empire to spread the teachings of Buddhism and promote social welfare. Ashoka's reign marked a significant period of peace, prosperity, and cultural exchange in ancient India.

In conclusion, the grandfather of Ashoka was Chandragupta Maurya, the founder of the Mauryan Empire. Chandragupta's achievements and administrative systems paved the way for Ashoka's rule, and Ashoka's reign left a lasting impact on Indian history.