According to the passage, which of the following posed the biggest obstacle to the development of military forts

A．It was expensive to import produce from far away.
B．Food brought in from outside was often spoiled.
C．Gardening was a way to occupy otherwise idle soldiers.'
D．The soil near the forts was very fertile.

A．they enjoy having one drink after another
B．they like the kind of drinks they get on the wagon
C．they are afraid of losing their self-control in drinking again
D．they are alcoholics and can not control themselves well