68. The enthalpy of formation of an element in its standard state is .
(A) the enthalpy of its reaction with oxygen.
(B) determined by its melting point.
(C) the enthalpy of its reaction with carbon.
(D) zero.
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統計: A(0), B(0), C(0), D(4), E(0) #2319885
統計: A(0), B(0), C(0), D(4), E(0) #2319885