Question

Revise the passage by changing all of the gerunds to infinitives and all of the infinitives to gerunds.

Answer 1

On the one hand, a gerund is a verb that acts as a noun, know for the -ing form. On the other hand, an infinitive is the basic form of a verb, that usually follows  "to" or another verb form.  The revised sentence, including both of these, is:

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

Answer 2

Answer:

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