The correct answer is - 4. Caliphs were able to spread Islam as far as Europe and India.
The Caliphs were of great importance for the spreading of the Islamic religion. In a very short period of time, they managed to spread the new religion in the Middle East, most of Central Asia, east to the northwestern part of India, and northwestern part of China, through North Africa, and even into Europe on Spanish soil. They created a huge Islamic territory that lasted for few centuries, until the Mongols managed to conquer them and destroy them.