Answer:
b. Constantinople was the Byzantine capital, and the empire was not able to survive its fall.
c. Trading routes and powerful defenses made Constantinople the richest city in the empire.
Explanation:
For b: Constantinople was the center of Byzantine culture, and was considered a multi-cultural, multi-ethnic and multi-religious city. These factor made it so influential, so rich and powerful.
For c: Merchants traded through the Mediterranean, east and west. They dominated and had the control of the main trading routes, so they made a fortune out of this activity.