1 The charge-density response function of a uniform two-component plasma is studied on the basis of the third frequency moment sum rule of its spectral function and the method of an equation of motion. An exact expression of the third sum rule is presented with emphasis on the existence of a singular term. It is found that available local-field theories for the response function do not satisfy this sum rule and any theory with frequency-independent local-field correction can not satisfy the

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... d-and the perfect screening-sum rules, simultaneously. The response functionD r ij(q,w) and the corresponding frequency-dependent local-field correction Gij (q,w) are calculated on the basis of the equation of motion. The obtained result yields a well-known relation between the pair correlation function and its radial derivative at r=O for large wave vectors and satisfies the third-and the perfect screening-sum rules.