Which of the following is not a past participle? a. found b. seen c. shrank d. driven

I would say c. shrank

The old have free hearts and free minds.

  i think you forgot to put the options but if your reffering to this question then your answer will be "b"  a. add "to" to the base form to create an adjective.b. when the subject of a sentence is singular, add "–s" to the base form.c. add "–ed" to irregular base forms to form the past participle.d. do not use a base form with plural subjects