Concept:Some English nouns form their plural with the suffix '-en' instead of the usual '-s' or '-es'.Explanation:The word 'Ox' is an irregular noun. Its plural is not made by adding '-s' or '-es'.Instead, the correct suffix is '-en', giving the plural 'Oxen'.This pattern also appears in other words like 'child' (children) and 'brother' (brethren).Thus, the suffix '-en' is the right choice here.Answer:Option A: -en