instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
question:
Three many families are known quarks divided into.
answer:
How many families are known quarks divided into?


question:
The bird ancestor that lived in trees developed wings, which is commonly associated with birds.
answer:
The bird ancestor that lived in trees developed what feature commonly associated with birds?


question:
A volcanic arc is formed when a subducting plate flows under another tectonic plate.
answer:

What is formed when a subducting plate flows under another tectonic plate?