Grammar question: substitute A for B

[Theoretician]

If a national newspaper editor told you to substitute A for B in a recipe that you've not yet seen, would you expect the original recipe to contain

a) A
b) B
c) could be either

Oh didn't see that the recipe was subsequently posted by op, on phone with patchy coverage.

Shall shut up now.

We know what both are.

Don't worry Through, as I said earlier, you got the grammar right in your first post, it was only after that you got a bit confused about what the question was.

I am old. I was taught proper.

The answer is B.