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.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.