Nouns in plural
German nouns are frequently altered significantly when moving from the singular to the plural form, and the alteration is sometimes more complicated than adding an "s" or an "es" as one would in English.
These transformations can involve the addition of an umlaut and the alteration of the word ending (example: das Buch, die Bücher). In some cases, the noun itself doesn't transform at all.
You will have to determine whether the noun takes an "n" or "en" ending; an "s", an "e", or an "er". Students of the German language often begin by memorizing frequently used nouns in their various forms.
In the sentences below, fill in the blank with the plural form of the noun given.