\( \begin{array}{lll} & & 3,458.9 \div \square \\ \text { A. } 10^{1} \\ \text { B. } 10^{2} \\ \text { C. } 10^{3} \\ \text { D. } 10^{4}\end{array} \)

To solve \(3,458.9 \div \square\), we need to find out which power of ten would result in a quotient that is close to 1, as that will help us determine the correct option. Dividing \(3,458.9\) by \(10^3\) (or \(1,000\)) gives us approximately \(3.4589\). Dividing by \(10^2\) (or \(100\)) gives \(34.589\), which is too high, and dividing by \(10^4\) (or \(10,000\)) yields \(0.34589\), which is too low. Therefore, the only option that keeps the quotient above 1 but reasonably close to it is \(10^3\). So, the answer is \( \text{C. } 10^{3} \).