B ∪ (C' ∩ A)
Starting from the inside, C' ∩ A is the intersection of not C, which is everything except the circle C, and A. That's the part I shaded in bright blue.
That's unioned with B, which is just all of the circle B. I shaded the parts of B that I didn't already shade with a grey-blue.
These should all be the same shade; I just made them slightly different for explanation.
