Which of the following are examples of preparation methods and techniques used for making 'Bechamel sauce'?

a) Melt cubed butter in a pan over medium heat until brown with a nutty scent
b) Add plain flour and stir continually to cook out the flour till light brown
c) Remove from the heat and slowly add in lightly-beaten egg whites
d) Gradually add lukewarm, full-cream milk and stir continuously with a whisk or wooden spoon