What grammatical rule is often applied when using the genitive case for living entities?

The use of the genitive case for living entities generally follows the guideline of indicating possession or a relationship through the use of an apostrophe. Specifically, when dealing with singular nouns, an apostrophe is placed before the 's' to show that something belongs to that person or entity. For example, "the dog's collar" indicates that the collar belongs to the dog, where 'dog' is a singular noun.

The other options do not accurately reflect the rules for the genitive case. While an apostrophe is indeed used, it is not limited to plural forms, and it can be necessary for proper nouns, so the generalization that excludes apostrophes for proper nouns or focuses exclusively on plural cases deviates from the correct application of the rule. Thus, using an apostrophe before the 's' for singular names remains the correct application in the context of the genitive case for living entities.