This site gives a very clear explanation of a gerund and its noun qualities. This resource explains how to use the possessive case with a gerund. A quiz is provided to check understanding of this concept.

In this writing and grammar tutorial, learn how to distinguish and use nouns and pronouns in English and whether they are subjective, nominative, possessive, or objective.

This instructional activity focuses on recognizing and demonstrating the standard use of apostrophes when using both singular and plural. It also provides a practice exercise.

This site focuses on the three uses for apostrophes: forming possessives of nouns, forming plurals of lowercase letters, and showing omission of letters and provides examples of each.