Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: When light passes from one medium to another, it changes speed.

A: When light passes from one medium to another, it changes what?
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Q: The bones of the newborn skull are not fully ossified and are separated by large areas called fontanelles.

A: The bones of the newborn skull are not fully ossified and are separated by large areas called what?
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Q: Electrostatic repulsions normally prevent a positively charged particle from colliding and reacting with a positively charged nucleus, but may be overcome by kinetic energy.

A:
What normally prevent a positively charged particle from colliding and reacting with a positively charged nucleus, but may be overcome by kinetic energy?
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