By the End of the Fourteenth Century,why Had Florence Become

By the end of the fourteenth century,why had Florence become an important banking city?

A) The Medici family began lending money to northern European countries.
B) Florence's hilltop location provided natural defense against thieves.
C) The pope conferred Siena's papal banking privileges on Florence.
D) Florence's metalworking guild controlled Europe's largest gold reserves.