The correct answer is C) it prevented pottery from cracking when fired.
The method of making pottery by using coils of clay was better than simply shaping the clay by hand in that this method prevented pottery from cracking when fired.
The coil method is when coils of clay are used to be bowls of different sizes and shapes. With your fingers flat, you roll into ropes1/4 or 1/2 thick to create the piece of pottery to you want. You keep adding the coils you need. The other methods of working with clay are Pinch Pots and the Slab method.
The other options of the question were a) the pottery could be cut or stamped with designs, b) it created a watertight seal and d) it produced more attractive pottery.