What is salad dressing an example of?
Depends what sort of salad dressing you're considering.....
If it's something like....balsamic vinegar, then its a homogeneous mixture. If, however, its vinegar/oil dressing, then it would be a heterogeneous mixture (both are liquid, but they are immiscible).
Dressings of vinegar with ground pepper and/or herbs in it would also be a heterogeneous mixture.