Concept:An opposite in meaning directly contrasts with the underlined word in context.Explanation:The underlined word is “compulsory,” meaning required or obligatory. The sentence says only question one is compulsory. So the rest of the questions are not compulsory. The word that means “available to be chosen but not obligatory” is “optional.” Thus, “optional” is the most nearly opposite and correctly fills the gap.Answer:D. optional