to the plural ending by an S , you just add ' except for irregular plurals as men's hats, children's toys , women's dresses .............. hope I helped !
Answer: The genitive case is commonly shown in Modern English nouns (3.) adding 's to the singular.
Explanation: The genitive case in Modern English is used to indicate possession, that is to say to indicate that something belongs to someone. <u>The genitive case is shown adding 's to a singular noun</u>.<u> For example, the genitive case of the noun "girl" is "girl's"</u>.<u> However, the genitive case of plural nouns is formed only by adding an apostrophe (')</u>. In that way, the only correct option is 3. adding 's to the singular.