There is no plural form for the word, countries. This word itself is a plural.
The plural of diary is diaries.
The plural form of the word 'deed' is 'deeds'.
The plural form of the word gelato is gelati.
The plural form of the word neurosis is "neuroses".
The plural of radius is radii
The plural form for the demonstrative pronoun this is these.
The plural form of the word "inferno" is "infernos."
The plural form of the word "ranch" is "ranches."
There is no such word as raduis. The radius of 64 depends on what 64 is a measure of!
There is no plural form for the word, countries. This word itself is a plural.
There is no plural word for if.
The plural form is data.
The plural form of the word "baby" is "babies."
The plural form of the word "pharynx" is "pharynges."
The plural form for the word 'pioneer' is pioneers.
The plural form of vow is vows.