Final answer:
Two nouns that exist in both singular and plural forms are 'child' and 'children', as well as 'mouse' and 'mice'. The verb must agree with the number of the noun, changing form for singular or plural as in 'A child plays' versus 'Children play'. With 'or' or 'nor', the verb agrees with the noun closest to it, as in 'Either the mouse or the cats are' or 'Neither the mice nor the cat is'.
Step-by-step explanation:
Two nouns which exist in both singular and plural forms are child (singular) and children (plural), as well as mouse (singular) and mice (plural). Understanding the correct form of a noun depending on its number is crucial for proper subject-verb agreement. For instance, the sentence 'A child plays in the park' uses the singular verb 'plays' because 'child' is singular, whereas 'Several children play in the park' uses the plural verb 'play' because 'children' is plural.
In cases where nouns are joined by the conjunctions 'or' or 'nor', the verb should agree with the closest noun in number. Examples include 'Either the mouse or the cats are responsible for the missing cheese' (plural verb due to the closer plural noun 'cats') and 'Neither the mice nor the cat is interested in the toy' (singular verb due to the closer singular noun 'cat').