The correct answer is option 'A', Keshav Chandra Sen.

Explanation:
Keshav Chandra Sen was a prominent figure in the Bengal Renaissance movement, which aimed at social and cultural reform in 19th century Bengal, India. He was a key leader of the Brahmo Samaj, a socio-religious reform movement founded by Raja Rammohan Roy.

During his time, Keshav Chandra Sen observed the state of the nation and expressed his thoughts on its current condition. He believed that the nation had fallen from its previous glory and was now in ruins. This statement reflects his concern for the degradation and decline of the society and the need for revival.

Here is a detailed explanation of the statement:

1. Historical Context:
- The 19th century was a crucial period in Indian history, marked by British colonial rule and the decline of traditional institutions.
- The British Raj had a significant impact on Indian society, economy, and culture, leading to the disruption of traditional systems and values.
- This period also witnessed the emergence of various reform movements, such as the Brahmo Samaj, aimed at addressing the social, cultural, and religious issues prevalent in society.

2. Keshav Chandra Sen and the Brahmo Samaj:
- Keshav Chandra Sen played a pivotal role in the Brahmo Samaj, which sought to reform Hindu society and revive its ancient glory.
- The movement advocated for social equality, women's rights, education, and the abolition of social evils like caste discrimination and child marriage.
- Keshav Chandra Sen, along with other leaders of the Brahmo Samaj, actively worked towards social and religious reforms.

3. Fallen Nation and Primitive Greatness:
- Keshav Chandra Sen's statement reflects his belief that India had fallen from its past greatness and was in a state of decline.
- The term "fallen nation" indicates the loss of the nation's former glory, which could be attributed to various factors such as colonial rule, social evils, and cultural degradation.
- The reference to "primitive greatness" implies that India had a glorious past, characterized by advanced civilizations, rich cultural heritage, and intellectual achievements.
- However, this greatness was now buried in ruins, suggesting that the nation had lost touch with its ancient wisdom and needed revival.

In conclusion, Keshav Chandra Sen's statement highlights his concern for the state of the nation during the 19th century. He believed that India had fallen from its previous greatness and needed to revive its ancient glory. This perspective aligns with the reformist ideals of the Brahmo Samaj and their efforts to address the social, cultural, and religious issues prevalent in society.