Write the next sentence in this paragraph:

How to make shortbread
Prepare the oven.
Preheat the oven to 160c (320f) and place a rack in the center position.
Add cool butter to a mixing bowl.

Choices:
(a). Take 115 g ( cup) salted butter on the cool side of room temperature, workable but not melting. Cut it into small chunks and add to a mixing bowl.
(b). In a small saucepan, cream the butter with the purpose of the recipe, beating it into the butter with a hand mixer. Add the milk, granulated sugar, and vanilla.
(c). After placing the dough, start piling-adding a few pinches of salt to the bowl with the dough. Mix the flour, baking powder, baking soda, and salt.
(d). Melt the butter and set the bowl aside. In a separate mixing bowl, cream the butter and shortening.
(a).