Which group of words is a sentence fragment?

Why witchcraft often the explanation for illness

What do the excerpts have in common? both point out the tragic nature of situations in which children make journeys without their parents. both describe what immigrant children must do to survive when traveling to the united states. both explain why most children want to leave central america without their parents. both indicate the tragic problems and their consequences that children in central america must face.

Which sentence you is an example of chronological structure in “the city without us”?