C. It had a great seaport.
There were actually five reasons:
1) Geography - Florence is the ideal place for trade because It can be reached both by land and by sea.
2) Wealthy Merchants - Florence is filled with patrons of arts.
3) Independent Government - Florence is a place where people can behave in certain manner and not be persecuted; unlike other countries
4) Liberal people - People liberal thoughts and manners result to progressive behavior.
5) Humanism - People in Florence believe that life should be lived to ones greatest potential; a way of honoring Gods' greatest creation.