The majority of an individual fungus lives "in" its food source. What characteristics of the fungal growth form make this a necessity?

A)Fungi have a high ratio of surface area to volume and are highly susceptible to dessication.
B)Fungi have a low ratio of surface area to volume and are highly susceptible to dessication.
C)Fungi require the stimulus of "pushing" through the substrate to stimulate growth.
D)Fungi require more nutrients than other organisms, and large amounts of nutrients can only be acquired by living in a host.