Mycorrhizae enhance plant nutrition mainly by
a. converting atmospheric nitrogen to ammonia
b. stimulating the development of root hairs
c. absorbing nutrients (and water) through the fungal hyphae
d. providing sugar to root cells, which have no chloroplasts

The answer is C. A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular host plant. They colonize the roots of vascular plants connect them, one to the other; and then send out their filaments, called hyphae, as much as 200 times farther into the soil than the roots they colonize.

the correct answer is primary!