<p style="">The correct answer is (C) would have improved</p><p style="">The sentence reads: "If the government had reduced personal income taxes, the national economy would have improved much more quickly."</p><p style="">This sentence is a third conditional sentence, which is used to describe hypothetical situations in the past that did not happen and their imagined results. The structure for third conditional is:</p><p style="">[If + Past Perfect], [would have + Past Participle].</p><p style="">In this case:</p><ul style=""><li>"If the government had reduced personal income taxes" is the hypothetical situation in the past that did not happen.</li><li>"the national economy would have improved much more quickly" is the imagined result of that situation.</li></ul>