The correct answer is option 'D', Turks.

Explanation:
The rise of the Turks as a powerful group on the Islamic scene occurred after the Arabs and Iranians. The Turks played a significant role in shaping the political landscape of the Islamic world during the medieval period.

1. Background of the Turks:
- The Turks were a nomadic people who originated from Central Asia.
- They had a rich cultural heritage and were known for their military prowess.

2. Emergence of Turkish Power:
- The Turks began to emerge as a powerful force in the Islamic world during the 10th century.
- They were initially employed as mercenaries by various Islamic rulers.
- Over time, they gained influence and formed their own dynasties, establishing their rule in different regions.

3. Seljuk Turks:
- The Seljuk Turks were one of the most prominent Turkish dynasties.
- They originated from Central Asia and migrated to the Middle East.
- In the 11th century, they established the Great Seljuk Empire, which encompassed a vast territory, including present-day Iran, Iraq, and parts of Central Asia.

4. Contributions of the Turks:
- The Turks brought stability to the Islamic world by establishing strong and centralized governments.
- They promoted trade and commerce, leading to economic prosperity.
- The Turks also patronized the arts, architecture, and literature, contributing to the cultural development of the regions under their rule.

5. Impact on Islamic Civilization:
- The rise of the Turks had a lasting impact on Islamic civilization.
- They played a pivotal role in spreading Islam to new regions, such as Anatolia and the Indian subcontinent.
- The Seljuk Turks also facilitated the spread of knowledge and learning, particularly through the establishment of madrasas (educational institutions).

In conclusion, the Turks emerged as a significant power on the Islamic scene after the Arabs and Iranians. Their rise to power brought stability, economic prosperity, and cultural development to the regions under their rule. The Seljuk Turks, in particular, left a lasting impact on Islamic civilization through their contributions in various fields.