Answer: The reason why this is an example of Ethos is because it uses someone that people trust to endorse a product.
Step-by-step explanation:
In this advertisement, they use Kobe Bryant (A once famous basketball player) to sell vitamin water. However, an ad doesn't always have to bring in someone famous in order to be using Ethos.
Let's say you see one of those toothpaste ads that has "9/10 doctors recommend our product" on it. That would also be Ethos, because it's a group of people in a professional field saying that a product is good for you.
If you have IXL, I suggest you to do a Pathos, Logos, and Ethos lesson on it. It really does help learning about the different types of propaganda.