1- Foxes: The plural form of "fox" has to add an -ed due to the word ending in the consonant "x".
2- Summaries: The plural form of "summary" has to drop the "y" since it is preceded by a consonant, and replace it for an "i", which should in turn be followed by -ed.
3- Rodeos- The plural form of "rodeo" merely adds a final -s because it ends in a vowel.
4- Bonuses- Since the singular form of "bonus" already ends in a final -s, in order to make the word plural a final -es has to be added.
