It depends on your definition of "active" and "passive". Formally, all your examples are "active" - they neither use the Vorgangspassiv (werden + Partizip) nor the Zustandspassiv (sein + Partizip). But they are all examples of "impersonal" constructions, which are semantically similar to the passive voice. So they can all be translated into English by passive voice constructions, for example. Call it whatever your teacher calls it. Or call it "impersonal construction". BTW, your English translation are not very exact, and you shouldn't judge the construction based on the English translation. 1) Man hat den Arbeiter entlassen = One has dismissed the worker. They let the worker go = Sie haben den Arbeiter gehen lassen. Note "one" as the English equivalent of "man" (Dat. "einem", Akk. "einen"), and the impersonal construction "to let go". While your translation is very natural, you can't conclude anything from "they". (2) and (3) don't have a direct English translation; your example translation into English uses passive voice. 4) You can look up questions about spelling in the Duden (http://www.duden.de). Both spelling variants are correct, "selbstständig" is the recommended way of spelling (http://www.duden.de/rechtschreibung/selbststaendig).

First: selbständig and selbstständig are both correct, selbstständig might be easier because it makes more sense: you can identify the two words it's made of. 1) Man is very common, you'll find it in practically every other German sentence that doesn't need to specify who does something. So in this way it is quite similar to the passive. Your example would be: Der Arbeiter ist entlassen worden. (present perfect, passive) They is the subject, worker the object which becomes the subject of the passive sentence... As for 2) and 3): those are a bit beyond me. Can you give examples for the two? Would definitely help...

Answer to the comment section of tefisa's post Well, I think the spacing doesn't work in comments as it does in normal posts. About the passive: 2) "Das kann so nicht gesagt werden." (yours is infinitive, where the normal subject noun is missing. It's more like an indirect passive) 3) "Das kann besser gemacht werden". In general you can say that passive in German is build most commonly like this, so with the modal verb "werden". There exist other possibilities as well but that are the most common, plain, simple passive forms in German. If you even can build the passive of a verb depends on its dynamic and if its more transitive and intransitive (so needing an direct object or not)... but this is deep linguistic which I'm no expert of, so there you'd need to see by yourself. If you have the German lvl to understand this wikipedia article (where many linguistical terms are used), try it http://de.wikipedia.org/wiki/Aktiv_und_Passiv_im_Deutschen ... if not, search for smth else^^"