MiddleGameExercise4/solution (version 1)
Although the lower right has been badly cut up, Black's strength at the top is just too much to bear, especially since the White group is weak too. A fortiori, c is not enough either.
White can resolve things locally by cutting through with and but once again, Black's strength prevails and with he takes up a grand position.
So, somewhat disappointingly perhaps, connecting at is the best option. The important cut at is still there and Black needs to deal with it.