Hi, Does "freshman/sophomore/junior/senior" also apply to high shcool grades? If so, that means in the U.S.there are four grades in high shcool as well as in college? But i remember in The Big Bang Theory, when penny says she spent four years in high shool, Sheldon asks her surprisingly and satirically:"you spent four years in high shcool?" so I'm so confused how many years you have in high shcool in the states and how we should use "freshman/sophomore/junior/senior"? Thank you!