Correct Answer:
D. Dar-ul-Arqam
Dar-ul-Arqam was the house of Arqam ibn Abi al-Arqam in Makkah. The Prophet Muhammad (PBUH) used it as the first secret centre for teaching and spreading Islam, making it the earliest educational institution in Islamic history. Suffa was established later in Madinah, Al-Azhar in Egypt (970 CE), and Nizamiyya in Baghdad (11th century).