Which sentence uses incorrect end punctuation?

a. the theme of lloyd alexander short story the stone is that change is necessary, but enjoyable part of life.

b. this story shows us that we have nothing to fear from getting older!

c. part of what makes life worth living is watching things change: of plants sprouting, children learning new things, and achieving goals through a lot of hard work.

d. why would maibon ever plant if there's never a harvest?