If I’d want to know how time someone spent studying something, for example medicine. I saw in some places that I need use, something like this: “How long have you been studying medicine for” But, I

Rafael

If I’d want to know how time someone spent studying something, for example medicine. I saw in some places that I need use, something like this: “How long have you been studying medicine for” But, I can’t understand why I need use FOR at end.