What is the author's attitude toward the single agent service

A．The routes of the caravans.
B．The management of the caravans.
C．The expenses of the caravans.
D．The modes of transportation.

A．Caravan trade started in the Middle East.
B．Caravan trade was well developed before sea trade.
C．Caravans were well organized.
D．Caravans were protected by local governments.