John Bagnall's nailed this one, but he doesn't quite explain why there are two possible endings. I strongly believe that anyone who's spent more than a couple of weeks in Japan will understand this intuitively. read more
To make a noun plural that ends in "o," the rule is to add only 's' if there is a vowel before the o. If there is a consonant before the o, then you add 'es.' So, the correct plural of mango is mangoes. read more