The plural of the word "system" is "systems"
That is the correct spelling of the plural noun "economies" (economic systems)
The plural way to spell studio is studios.
The plural is hooves.
The plural is cherries.
The plural is cantaloupes.
The plural is resources.
The plural is "emeralds."
The plural is roses.
The plural form for the noun system is systems; the plural possessive form is systems'.
The plural is bridges.
Trout is plural
The plural of beach is beaches.