[giornogiovanna]

The correct merge, in my opinion would be D:

    add z w = z + w

My justification is that if you put each identifier on a separate line like this:

    fn add(
        x: i32,
        y: i32,
    ) -> i32 {
        x
        +
        y
    }

then as far as I know, Git would happily merge B and C into D.