<p><span style="font-size: 13.008px;">In this sentence, we are referring to a past action of the US unemployment rate decreasing. Therefore, we need to use the past tense form of the verb "decline". The correct answer is (A) declined. </span></p><p><span style="font-size: 13.008px;">(B) "declining" is in the present participle form, which is used to show an ongoing action. This does not match the past tense context of the sentence. </span></p><p><span style="font-size: 13.008px;">(C) "decline" is in the base form, which is used for general statements or commands, but not for specific past actions. </span></p><p><span style="font-size: 13.008px;">(D) "will decline" is in the future tense, which does not match the past tense context of the sentence.</span><br></p>