This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to make bechamel sauce
This is the basic recipe for bechamel sauce.
Place 2 tablespoons of butter in a small saucepan.
Heat the butter over medium heat until it's melted.

Pick your answer from:
(a). Always keep the ratio of butter to flour equal, regardless of whether you are producing a thinner or thicker sauce. Mix in 2 tablespoons of flour to make a roux, or the beginning stage of the sauce.
(b). Stir in the red pepper flakes. Cook the sauce until it thickens.
(c). Place 1 cup of the flour into the butter, along with the dry ingredients. Mix the flour and the water together.
(d). Add the bechamel and let it melt. Whisk in 3 cups (0.14 liters) of water.
The answer is:
(a).