They can go pretty fast on a flat road but any kind of hill and they obviously slow down . Ever overtaken one of these things ? Only then would you know how it plays with your nerves to start with !

Question: Why might these slow down on any kind of hills ?
Answer: These things might slow down on hills because they 're overpowered .None of the above choices .These things might slow down on flat roads because they 're underpowered .These things might slow down on hills because they 're underpowered .