Demonstrations.
There were a lot of police at the demonstration.
The noun forms for the verb to demonstrate are demonstrator, demonstration, and the gerund, demonstrating.
There are two accepted forms of the noun: adviser and advisor.The plural forms are advisers and advisors.The plural possessive forms are advisers' and advisors'.
Verbs don't have plural forms.
plural forms are uteri or uteruses.
There are two accepted plural forms of the noun vertex: vertices and vertexes.The plural possessive forms are vertices' and vertexes'.
The plural forms thesauruses and thesauri are both acceptable forms of the word thesaurus.
The plural forms for the singular lumen is lumina or lumens, both are accepted plural forms.
There are two accepted plural forms for the noun cargo, they are cargoes and cargos.The plural possessive forms are cargoes' and cargos'.
Singular. Plural is: they are, have and do.
German plural forms are formed irregularly.
Derogatory is an adjective, and has no plural forms.