The round cake was cut using a rectangular grid, the outer pieces were different shapes and sizes.

what is the best way to rewrite this sentence?
a. the round cake was cut using a rectangular grid: the outer pieces were different shapes and sizes.
b. the round cake was cut using a rectangular grid, but the outer pieces were different shapes and sizes.
c. the round cake was cut using a rectangular grid, so the outer pieces were different shapes and sizes.
d. the round cake was cut using a rectangular grid, because the outer pieces were different shapes and sizes.