7 Segment Display Segment C Kmap Confusion
All of your solutions are correct. You have covered all the 1 cases in valid terms, and not covered any 0 cases.

However, of them, the last one is closest to optimal. It uses the fewest terms, and its terms are the simplest. It's possible to optimize it slightly by "expanding" one of the terms.


   Specifically, the red term can be expanded to the left, changing it from b⋅c to simply b. This makes the formula b + c̅ + d.