Final answer:
The Islamic empire at its height extended from Spain to India, making it the largest empire the world had seen until that time. Option B is correct.
Step-by-step explanation:
The extent of the Islamic empire at its height was immense, reaching from Spain to India. At the zenith of its power, it surpassed other historical empires in size, even those of Alexander the Great, the Romans, and the Han Chinese.
The Islamic Caliphate expanded westward as far as Spain and Portugal and eastward to the Indus River valley, making the correct answer to the question B. From Spain to India. Not only did this expansion cover a vast geographic area, but it also meant the inclusion of a vast array of cultures, languages, and ethnicities within the empire's domain.