Answer: ABD (3rd choice)
Reason:
To name a plane, we pick 3 points on the plane that are not collinear. This means the points cannot fall on the same line. This rules out ABC. Infinitely many planes could pass through those collinear points, when we want exactly one unique plane defined.
ABD works out since points A,B, and D are in the plane and aren't collinear. Exactly one and only one plane passes through these three noncollinear points.
Saying ABCD is correct, but it's a bit overkill to include a fourth point when 3 will suffice.
We cannot involve N as part of the naming format since N is not a point. It's the label of the plane overall. This rules out NBD.