1. This answer was edited.

    Parent is a singular noun, so here it will be "Parent's house". When it is both parents (i.e. plural), it will be "Parents' house" The position of the apostrophe makes all the difference.

    1. Parent is a singular noun, so here it will be “Parent’s house”.
    2. When it is both parents (i.e. plural), it will be “Parents’ house”

    The position of the apostrophe makes all the difference.

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