All of the above are true.
A is correct, because, well. We can’t see atoms directly, at least not with our current levels of technology.
B is correct because a model is a representation of something by nature.
C is correct because our knowledge of the atom is still growing, and as we still don’t know about some future atomic developments, it’s called a model so that there’s still flexible room for new discoveries.
Hope this helps!
Bias can be present in a secondary source because it can be altered or changed. Secondary sources are after the event in question has taken place therefore MORE open to change, subjectiveness.
