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? 
 The round cake was cut using a rectangular grid: the outer pieces were different shapes and sizes.
 The round cake was cut using a rectangular grid, but the outer pieces were different shapes and sizes.
 The round cake was cut using a rectangular grid, so the outer pieces were different shapes and sizes.
 The round cake was cut using a rectangular grid, because the outer pieces were different shapes and sizes.