All of the above are true.
A is correct, because, well. We canβt 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 donβt know about some future atomic developments, itβs called a model so that thereβs still flexible room for new discoveries.
Hope this helps!