Could any of these be considered passive? I don't quite understand the concept of passive voice.
These are only parts of sentences so it is difficult to say if the whole sentences are Passive or Active.
The sense of Passive Voice is to change the object of a sentence to a subject of a new one.
For example let's analyze following 2 sentences:
- Ann wrote a letter.
- A letter was written (by Ann).
In the first sentence its subject is a doer (the person who wrote the letter), while in the other sentence the object created (a letter) becomes the subject.