Salve Regina
Above is an example of how this plainchant would have been written in the 5th century. This also gives us an idea of how written music evolved. Below is how we might be written today, but there are no rules about this. It could be written any way. This is the only set song on your course that has no key signature and no pulse.
Preab san Ól
Above is how Preab san Ól would usually be written, but below is another way it could be written depending on how it's sung. It could also be written in any key depending on the singer. Here it's written in G. However you can't mix this up with any other set song as it's the only one in 3/4 time!