it's plural because it has a 's' at the end.
Lifeguards is the plural form.
The noun 'lifeguard' is a singular noun. The plural form is lifeguards.
The possessive form for the noun lifeguard is lifeguard's.
Bridges is the plural form of bridge.
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
There is no plural form for the word, countries. This word itself is a plural.
"Groceries" is the plural form of "grocery."
The plural form of "meter" is "meters."
The plural form for the noun sergeant is sergeants; the plural possessive form is sergeants'.
It has no plural form.
The plural form of rung is rungs.
The plural form of parenthesis is parentheses.