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.