Which sentence best reflects the purpose for the line of reasoning identified in

To give is one of the best things people can do. Volunteering their time shows what caring people they are

Explanation: "Giving" is an example of a gerund, as it is a verb ending in -ing. To change this to an infinitive, you must use the base of "giving", which is "give". In this case, it is, "to give". "To volunteer" is an example of an infinitive. To change this to a gerund, add -ing to "volunteer".