In the US, College is never (or, almost never) secondary school, but only higher education. More specifically, college is a stand-alone undergraduate institution (2 or 4 year) or the undergraduate section of a university, or one of several subsections of a university (e.g. college of science, college of fine arts); or the buildings of such an institution. http://www.dictionary.com/browse/college
Clearly, in the UK, it can be secondary education.
As duolingo accepts both UK and US usage, "college" should be accepted here (despite the fact that it's not a correct match, in US english).
In the UK, Higher Education is restricted to degree courses, BSc/BA, MSc, PhD etc. A post-school college with a 2 yr course would be Further Education, but my point was that the term College is probably more frequently used in the UK for the more senior years at secondary schools, 6th form and equivalent.
«ficar» é muito mais comum do que «estar»; de qualquer forma, acho que não usar-se-ia «estar» mas sim «ser», como os prédios/edifícios estarão no mesmo sítio e, geralmente, permanentemente
EDIT: Na realidade, é muito comum perguntar onde «está» o supermercado, os correios, etc. em Portugal