Protein kinase is an enzyme that promotes phosphorylation of target proteins at specific sites, whereas protein phosphatase catalyzes the removal of a phosphate from a phosphorlated protein. phosphorylation and dephosphorylaytion can function as an on-off switch for a protein's activity, most likely through: A) the removal of one or more peptides
B) A change in the active site structure
C) A change in the optimal temperature at which a chemical reaction will occur
D) A change in the optimal pH at which a reaction will occur

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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.