Network+ Question

chemaster

There's a question on the sample exam on this site that asks:

27. At which of the following layers does SMTP operate?

The reference materials indicate that SMTP is on 3 layers: Sesson, Presentation and Application.

However, the exam key here indicates that the correct response is the Application layer.

Question: Is my current reference material totally wrong OR do we always select the top layer if multiple layers actually apply?

Thanks,