I'll try to tackle your question but, as a non-native speaker, I'm struggling with some of them too... 1- I have never taken her math classes. 2- He has been in his grandfather's house since last week (you do not need "the" here). 3- Basically, two options are possible. 3a) They have been working for Apple for more than one year (up to now - meaning they still work there. The Present Perfect Continious is used to emphasise how long you've been doing something - for more than one year). 3b) They worked for Apple for more than one year (it's in the past, they don't work there anymore). You usually work FOR a company but IN a field, like in finance, in engineering etc. 4- Were you awake when Fabio called? You can't use the Present Perfect here since it's obviously in the past (past is the time point at which Fabio called). As to the article "the" - well, in a general case, you wouldn't use it with a person's name. Unless it's this case: "- Fabio just called. - The Fabio who we saw yesterday at the party?" Here The = that particular. 5- Did they build the building, before the houses? - Hmm, I can't give you proper advice here but, anyway, it should be in the Past Simple Tense as well. It seems to me, there's something wrong with "before the houses"... Do you mean they built the houses first and then they built the building? In this case, I guess, it's better to say Did they build the building before they BUILT the houses? Hope this helps a little.