can a complex math equation can create multiple closed area? example : equation of circle can easily represent case A.
can some single complex mathematical equation can create case B ?

Yes, two curves can be represented with a single equation joining them as their product.Right hand sides of the individual equations should be  zero  before multiplying.
Multiple curves can be drawn on same x-y plane. We can visualize them together or separately. Draw graphs of two or three curves separately on transparent plastic sheets. Superimpose the sheets along their respective axes coinciding them onto a common origin.
The single product equation you get is valid representation for what all curves in the set you see.
