grrrrgrammar

Most nouns ending in O preceded by a consonant take –es in the plural:

hero-------heroes

potato-----potatoes

But some nouns of foreign origin and abbreviated words ending in O add –s only:
piano------pianos

solo--------solos

dynamo-----dynamos

photo-------photos

demo-------demos

All nouns ending in O preceded by a vowel take –s in the plural:

radio-------radios

cuckoo-----cuckoos

studio------studios