Answer:
The statement that best describes the spread of Islam under the first four caliphs is Arabs united under Islam and defeated nearby empires.
Step-by-step explanation:
As for the others if you need help....
1. B) Arabs united under Islam and defeated nearby empires.
2. B) Weakened Persian and Byzantine rule and C) Darling, effective fighting methods.
3. D) The Umayyads expanded into Spain.
4. B) Persian traditions strongly affected the caliphate. and D) Non-Arab Muslims were allowed to hold powerful positions.
5. D) It introduced them to a wide body of medical knowledge and the idea of training physicians and creating hospitals.
6. A) Chivalry and the romance of nomadic life.
^These should all be confirmed correct as of 12-14-21 for connections. Hope this helps! :D