By adding –s to nouns ending in -o

Singular	Plural		Singular	Plural
bamboo	bamboos		ratio	ratios
casino	casinos		scenario	scenarios
commando	commandos		silo	silos
disco	discos		shampoo	shampoos
duo	duos		solo	solos
dynamo	dynamos		stereo	stereos
ghetto	ghettos		studio	studios
kangaroo	kangaroos		tattoo	tattoos
kilo	kilos		trio	trios
photo	photos		video	videos
piano	pianos		zero	zeros
radio	radios		zoo	zoos