If the ph of the body gets too low, below 7.4, acidosis results. acidosis is serious because many of the chemical reactions that occur in the body are ph-dependent. if the body's ph drops below 6.8 or goes above 7.8, death may occur. because of this, we have buffers in the blood to protect against large changes in ph. as seen in the above reaction, the human buffer system depends on the fact that

Carbon dioxide released from tissue dissolve in the blood plasma to form carbonic acid.It is the best buffer system since it partially dissociates to hydrogen and bicarbonate ions (conjugate base). The amount of H+ ions directly influence the pH. Therefore, the forwards and reverse reactions (catalyzed by carbonic anhydrase enzyme) influence the pH homoeostasis of the body.   

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.