Answer: The correctly spelled plural forms are: men, hours, allies, go-betweens and runners-up.
Explanation: The plural form of a noun is usually formed by adding "-s" or "-es" at the end of the word. This is the case of the noun "hour" and the compound noun "go-between", whose plural forms are "hours" and "go-betweens" respectively. However, in other cases, irregular nouns are made plural by changing a vowel. For instance, the plural form of the noun "man" is formed by changing the "a" to "e": "men". Moreover, in order to form the plural form of a noun ending in "y", such as "ally", the final letter is usually changed to "i". Therefore, the plural form of "ally" is "allies". Finally, the noun "runner-up" is made plural by adding the "-s" after "runner": "runners-up".
