Multi-choice problem: Continue writing the next sentence in this paragraph:

How to make washing soda
Gather your supplies.
You will need a large metal baking dish (though stone or glass will also work), a one-pound (454 grams) box of baking soda, and a wooden spoon.
Preheat your oven to 400 f (204 c).

Available choices: a. Grease a baking dish and line it with parchment paper. Combine 1 1/2 cup (120 ml) baking soda , 1/2 cup (240 ml) of white vinegar, and 1 tbsp.; b. If you have a stovetop, the closer you get to the temperature, the more quickly it will sink. Mix the powdered sugar with the baking soda.; c. Spray your baking dish with non-stick spray to prevent sticking to the bottom. You can also use a bottle of non-stick spray, which you can find online or at your local craft or food supply store.; d. Cover the bottom of the baking dish with a thin layer of baking soda. Baking a thinner layer that's about one-quarter inch (0.6 cm) thick will ensure that the process occurs uniformly.;
d.