Concept:The word "vacuum" has a double 'u' but only one 'c'.Explanation:Option A: Vacuum is correct. It has one 'c' and two 'u's.Option B: Vacum is wrong because it is missing one 'u'.Option C: Vaccum is wrong because it has an extra 'c'.Option D: Vaccuum is wrong because it has extra 'c' and extra 'u'.So only Vacuum follows the standard spelling.Answer:A. Vacuum