Answer:
B, Caravansaries
Step-by-step explanation:
The Muslims often used caravansaries because to travel through the desert, they didn't want to carry it by hand and also a letter would have taken a very long time to travel. The person would have gotten to their destination before the letter got there!
A Sharia wouldn't have helped because it is a part of the Muslim religion. It is part of the teachings of the Koran and the teachings of the Prophet.
Market inspectors are kind of like the managers of the company. These wouldn't have helped in carrying gold over the great distances.
Therefore, caravansaries would be the only logical answer!