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Below are the choices that can be found elsewhere:
a. [CH3NH-] * [OH-] / [CH3NH3+]
b. [CH3NH3+] / ([CH3NH2] * [OH-])
c. [CH3NH3+] * [OH-] / [CH3NH2]
d. [CH3NH3+] * [OH-] / [CH3NH2] * [H2O]
The answer is C.