Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The plural form of the noun museum is museums.The plural possessive form is museums'.Example: All of the museums' hours are posted on the main website.
singular
The singular noun is museum, the singular possessive form is museum's.The plural noun is museums, the plural possessive form is museums'.
Musea is an acceptable form for the plural but museums is used more often.
The museum's exhibit is wonderful.The museum's exhibits are wonderful.Is for singularAre for plural
The singular noun is museum, the singular possessive form is museum's.The plural noun is museums, the plural possessive form is museums'.
In the sentence, "The local museum is extending their hours for the summer."The pronoun is their, a possessive adjective describing the noun 'hours'. The antecedent is the noun 'museum'.The plural pronoun 'their' is used for the singular antecedent 'museum' to represent 'the people in charge of the museum'. It would also be correct to say, "The local museum is extending its hours..."
The word CAMIO (Catalog of Art Museum Images Online) is an acronym which has no plural and the name of some businesses such as Camio Security Alarm Systems.Perhaps you were thinking of the noun cameo, a decorative carved gem or other stone; the plural for the noun is cameos.
The noun passes is the plural form for the singular pass. Example: The museum passes for the students are here. The word passes is also the third person, singular, present of the verb to pass.
The word "create" is a verb-- to create. In English, verbs do not have plurals. For example: I create my sculpture. Three hundred students create their sculptures. It is only a noun that has a plural. The noun form of "create" is "creation." There are many artistic creations in the museum.
There is no specific collective noun for steam engines, in which case any noun suitable for the context will work; for example a collection of steam engines, a display of steam engines, a museum of steam engines, etc.