The impact of al-Mansur on Islam is best captured by option B: He moved the capital of the Abbasid Dynasty to Baghdad and unified the kingdom.
Al-Mansur (714–775 CE) was the second caliph of the Abbasid dynasty and is often credited with establishing Baghdad as the capital of the Islamic empire. This move not only centralized administration but also made Baghdad a cultural and intellectual hub of the Islamic world. Under his rule, the city became a center for trade, learning, and culture, fostering advancements in science, literature, and philosophy. Al-Mansur's leadership helped unify the diverse regions of the Abbasid empire, strengthening its political and social structure.
While he did support scholarship and the translation of texts (which is referenced in option D), his most significant contribution was indeed the establishment of Baghdad and the political unification of the empire.