Which sentence is punctuated correctly?

A) The soup which was my mother's recipe overflowed on the stove and made a big stain.
B) The dog, that had never been trained, ended up winning the training portion of the dog show.
C) The envelope, which had no return address, was sitting on the table at the foot of the staircase.
D) The dolphin, with the scar on its back, was quickly identified by scientists as having traveled over 1000 miles in a month.