How do you make a word plural that ends in o and is proceded by vowel?

You're right to ask, because this is one of those tricky areas of English grammar!

For words ending in "o" preceded by a vowel, you typically add "-s" to form the plural.

Here are some examples:

* Radio - Radios

* Studio - Studios

* Zoo - Zoos

Exceptions:

There are a few exceptions, like the following:

* Albinos (not "albinoes")

* Cacti (not "cactuses")

* Clichés (not "clicheos")

* Folios (not "folioes")

* Halos (not "haloes")

* Memos (not "memoes")

* Pharaohs (not "pharaohoes")

* Photos (not "photoes")

* Profs (informal) (not "profoes")

* Solos (not "soloes")

* Stereos (not "stereoes")

* Vetoes (not "vetoees")

Note: These exceptions are more common in American English. British English often uses "-es" for these words.

In doubt, always check a dictionary!