Concept:The missing word must be the closest opposite of the underlined word and also make sense in the sentence.Explanation:The underlined word suggests laziness or lack of effort.The sentence therefore contrasts idleness with steady, careful work."Diligence" means careful and persistent hard work, so it directly opposes laziness."Prudence" means caution, "attentiveness" means watchfulness, and "sharpness" means keenness; none of these express the opposite of laziness.Answer:C. diligence