Directions: Pick the odd one out.

Potato, hero, memo, mango, volcano

Correct. The four words - potato, hero, mango, and volcano – follow the same rule while forming the plurals (by adding –es to the singular). (Rule: If the singular noun ends with –o and the –o has a consonant before it, add –es to form the plural of the word.) Thus, the plural forms of these words are - potatoes, heroes, mangoes and volcanoes. The word ‘memo’ is an odd one here since it is an exception to the rule and forms the plural by adding –s to the singular noun (memos).