Sep 22, 2016 - 01:33 PM
Hi, Karen, good question! "Casa" is a bit special and it's not always used with the article when referring to someone's house. You can either say "La cena en casa de Sandra" or "en la casa de Sandra". Both are correct and perfectly natural. However, when talking about one's own house we usually say "Estoy en casa = I'm at home" rather than "Estoy en la casa" (although this is correct too). In all other cases you'd use an article, as in "Está en la casa blanca". In the program we sometimes use "casa" without an article, but in translation exercises both options should be accepted. Hope this is clearer now!