When determining a level of confidence, which is the correct order of authorities in order of general persuasiveness $($most authoritative to least authoritative$)?$

a$.$ Tax treaties$>$Final regulations $>$Revenue Rulings and revenue procedures

b$.$ Court cases$>$Final regulations$>$Revenue Rulings and revenue procedures

c$.$ Private letter ruling$>$Notices and administrative pronouncements$>$Tax treaties

d$.$ The Internal Code$>$Final regulations$>$Court cases