Making Chocolate Cake

The students were on a page in their textbook which illustrated the steps on how to make a chocolate cake. In the diagram, the flour was labelled as 'SR Flour'.

Student A: Teacher, what's SR?

Teacher: Right, class. Can anyone guess what SR stands for?

Student B: Secret recipe flour, teacher!

Teacher: *lol* Erm... No, it's not secret recipe flour. Take another guess.

Student C: Self-raising.

Teacher: Self-raising flour. That's right!